Only if 在这个题里为什么不用虚拟

if only: 要是...多好
Examples:
1. If only he had been here.
要是他当时在这儿就好了.
2. I dread the coming exams. If only I could have time to review my lessons.
我对即将到来的考试非常担心.如果我有时间复习该有多好啊.
3. If only I had another chance.
要是我再有一次机会就好了.
4. I am so tired. If only I can take the day off tomorrow.
太疲倦了.如果明天能不上班多好.
5. If only problems would come one at a time!
要是问题一次只发生一个该多好!
6. If only it clears up, we'll go.
只要天一放晴,我们就去.
7. If only one had an unlimited supply of money!
要是财源不断就好了!
8. She would be a very good player if only she could get it together.
她若能控制得当就能成为很好的选手.
only if:
conj. 只有当(只是在...的时候)
Examples:
1. The company will succeed only if it have sufficient backing.
只有当该公司获得足够的资助,它才会成功.
2. A compound proposition that has components joined by the word and or its symbol and is true only if both or all the components are true.
综合命题由和或其符号所连接的子句组成的复合命题,只有当所有子句为真时,该句才为真
3. I can buy the house only if a mortgage for 2000 dollars is available.
只有拿到两千美元的抵押贷款,我才买得起那栋房子.
4. Only if I get a job will I have enough money to go to school.
我只有找到了工作才有足够的钱上学.

if only:要是...多好
Examples:
1.If only he had been here.
要是他当时在这儿就好了.
2.I dread the coming exams.If only I could have time to review my lessons.
我对即将到来的考试非常担心.如果我有时间复习该有多好啊.
3.If only I had another chance.
要是我再有一次机会就好了.
4.I am so tired.If only I can take the day off tomorrow.
太疲倦了.如果明天能不上班多好.
5.If only problems would come one at a time!
要是问题一次只发生一个该多好!
6.If only it clears up,we'll go.
只要天一放晴,我们就去.
7.If only one had an unlimited supply of money!
要是财源不断就好了!
8.She would be a very good player if only she could get it together.
她若能控制得当就能成为很好的选手.
only if:
conj.只有当(只是在...的时候)
Examples:
1.The company will succeed only if it have sufficient backing.
只有当该公司获得足够的资助,它才会成功.
2.A compound proposition that has components joined by the word and or its symbol and is true only if both or all the components are true.
综合命题由和或其符号所连接的子句组成的复合命题,只有当所有子句为真时,该句才为真
3.I can buy the house only if a mortgage for 2000 dollars is available.
只有拿到两千美元的抵押贷款,我才买得起那栋房子.
4.Only if I get a job will I have enough money to go to school.
我只有找到了工作才有足够的钱上学.

so long as；provided；as far as ;as long as ;so as

他说爱你到骨髓:(爱到极限了):你的问题可以有以下解释和理解.








主句可以倒装.但不绝对!
Only if 条件从句在前,中间无逗号时主句要倒装!


Only if you have interested in learning,you will learn well. 是对的!
You will learn well only if you have interested in learning. 是对的!

Only if you have interested in learning will you learn it well.主句倒装,也是对的!


主句要倒装

Only if I get a job will I have enough money to go to school.
我只有找到了工作才有足够的钱上学.
Only if a teacher has given permission is a student allowed to enter this room.
只有得到教师的允许,学生才可以进这间屋.
Only if presented in this way can your idea get over to the audience.
只有用这样的方式提出来,你的意思才能使听从明白.


主句不用倒装
Our prices are in force only if you order by return mail.
我方价格仅以你方速复我订货,才有效.
The company will succeed only if it have sufficient backing.
只有当该公司获得足够的资助,它才会成功.
I can buy the house only if a mortgage for 2000 dollars is available.
只有拿到两千美元的抵押贷款,我才买得起那栋房子.
You can make progress only if you are modest.
惟虚心乃能进步.
Accept a drink only if you really want one.
只有在你真正想喝酒的情况下,才能接受一杯.

You would be able to know that happiness is far too valuable only if you have experienced many hardships.
He has been concentrated on the development of his career in the past five years.
The final decision depends on the next year's economic situation, meanwhile, we should continue to work at present.
Not only I do'nt object to interest in photography,but have majored in photography class to improve my techniques for photography during my college days.
Tell the truth,I didn't sleep for two days and nights before the deadline so as to finish the task.

If only 表示虚拟语气,如
If only I were you!如果我是你.
If only (expressing a strong wish表示强烈的愿望)但愿,真希望,只要...就好了：
If only he wouldn't eat so noisily.但愿他吃东西不这样大声就好了./If he would only learn to eat quietly!但愿他学会吃东西时小声点就好了!
only if 表示条件,只有.
only if表示"只有"；if only则表示"如果……就好了".If only也可用于陈述语气.
I wake up only if the alarm clock rings. 只有闹钟响了,我才会醒.

答案选A 此题考察only if置于句首要到装的知识点（only if可以引导倒装句,意为：只有.才.） 翻译：你只有学习才能通过这门课.

只有当.前面讲干什么事,后面讲条件

if only
只要；要是…多好
If only I could see him.
要是能见到他就好了
only if
只要……就；只是在……的时候
Only if she help me,can I succeed.
只要得到她的帮助我就能成功

only if 除非
if only如果
what if如果…将会怎样,
even thougheven though 即使,尽管
held my peace,even though I wanted to tell her exactly what I hough.
即使我本想把我的看法如实地告诉她,我也没开口.

我觉得,是因为这个句子中有逗号把这个句子隔开了,所以用法就不同了.
例如,Only if you eat the correct foods will you be able to keep fit and stay healthy.这个就得用倒装.
我觉得这个就很像在非限制定语从句中,“,+which"和把逗号后面加上“and"后用法会不一样同一个道理.
个人拙见.
PS 主语从句就是一个从句作为一个句子的主语,引导主语从句的关联词有：that,what,where,when,why,who,whether,how,whatever,wherever,whenever,whoever,and however.（最后这条引用别人的.）

我突然想到我要做一个演讲 sth occur to sb 某人突然想起某件事 所以应该是
Making a speech suddenly occurs to me .
only if 只有在……的时候,表示对条件的强调 放于句首需要倒装 所以应该是
Only if making（主谓结构-非谓语） up your mind can you continue your career
希望能帮助到你,谢谢采纳.

after all 毕竟
. You should forgive him for his forgetfulness; after all, he is over seventy.
你应该原谅他的健忘症,毕竟他已经七十多岁了.

2. You should be charitable with him; he is a child after all.
你应该对他宽容些,毕竟他还是个孩子.
3 Don't blame him for breaking that vase; after all he is a child.
别怪他打碎那个花瓶, 他毕竟是小孩子嘛.
only if:
只有当(只是在...的时候)
1. The company will succeed only if it have sufficient backing.
只有当该公司获得足够的资助,它才会成功.

2. A compound proposition that has components joined by the word and or its symbol and is true only if both or all the components are true.
综合命题由和或其符号所连接的子句组成的复合命题,只有当所有子句为真时,该句才为真

3. I can buy the house only if a mortgage for 2000 dollars is available.
只有拿到两千美元的抵押贷款,我才买得起那栋房子.

only if
conj.只有当(只是在...的时候)
用法：置于句首时,主句要倒装.
例句：
Only if I get a job will I have enough money to go to school.
我只有找到了工作才有足够的钱上学.
The company will succeed only if it have sufficient backing.
只有当该公司获得足够的资助,它才会成功.
I can buy the house only if a mortgage for 2000 dollars is available.
只有拿到两千美元的抵押贷款,我才买得起那栋房子.
A compound proposition that has components joined by the word and or its symbol and is true only if both or all the components are true.
综合命题由和或其符号所连接的子句组成的复合命题,只有当所有子句为真时,该句才为真
ps：
if only 要是...多好（多用于虚拟语气中）
例句：
If only it clears up,we'll go.
只要天一放晴,我们就去.
If only problems would come one at a time!
要是问题一次只发生一个该多好!
If only he had been here.
要是他当时在这儿就好了.
If only one had an unlimited supply of money!
要是财源不断就好了!
If only I had another chance.
要是我再有一次机会就好了.
I am so tired.If only I can take the day off tomorrow.
太疲倦了.如果明天能不上班多好.
I dread the coming exams.If only I could have time to review my lessons.
我对即将到来的考试非常担心.如果我有时间复习该有多好啊.
She would be a very good player if only she could get it together.
她若能控制得当就能成为很好的选手.

1,only if相当于if的加强版,引导条件状语从句,意思是[只有在.的“假设”条件下],那么它虚拟语气形式和if是完全相同的,关于If引导的与“事实相反的条件状语从句“的虚拟语气在各时态的变化形式,如果不清楚请看百度文库,都有很详细讲解.
2,if only的意思是”如果.就好了“,它的意思等同于wish,表达与事实相反或可能性不大的愿望时,虚拟语气形式同wish.与only if的虚拟语气形式有不同,不清楚wish怎么虚拟也请看百度文库.
ps最大的区别就是only if引导主-从结构,而if only相当于一个句子中的状语,不是从句的引导词.

only if表示"只有"；if only则表示"如果……就好了".If only也可用于陈述语气.
I wake up only if the alarm clock rings.只有闹钟响了,我才会醒.
If only the alarm clock had rung.当时闹钟响了,就好了.
If only he comes early.但愿他早点回来.
辨析only if 与 if only
only与if这两个单词随意组合,可以组成两个意义相近,但用法不尽相同的短语only if与if only.现将它们的具体用法辨析如下：
一、only if意为“only on the condition that,as long as”,“只要；假如”.它用于陈述事实或必要的条件,比if所表达的语气更强烈.
You'll pass this course only if you study.只要你学,你就会通过这门课.
Children may enter the club only if they are accompanied by adults.只要孩子们有大人陪同就可以参加俱乐部.
The students at the university can take up part-time job only if it doesn't interfere with their studies.只要不影响学业,这所大学的学生可以从事兼职工作.
二、if only则有两种含义.第一种含义与only if近似,意为“as long as”,“只要”.例如：
If only it clears up,we'll go.只要天一放晴,我们就去.
第二种则是“expressing a wish or assumption”,“但愿；如果……就好了”.它用来表达一个不可能实现的愿望或假设,句子要用虚拟语气.例如：
If only she would come!要是她能来就好了!
If only you had told me you had a spare ticket for the show.如果你告诉我,你多了一张演出票就好了.
If only you had worked with greater care!你要是工作更仔细一些该多好!
如果有帮到您 如果还有问题 请重新提问哦

简单来说,两个都可以用于引导条件从句.但是if only 用的是虚拟语气.
以下是详细解说：
Only if和if only的用法区别
一、only if
1.在only if 这个短语中,副词only是中心词,而从属连接词if则只是用来连接从句的,因此,它表示“只有……(才)；只有在……的时候,唯一的条件是……”的意思.例如：
I told him he would succeed only if he tried hard.我告诉他,只有努力才能成功.
2.only if 有时也写成only...if,表示唯一的条件,但是意思不变.例如：
I will only come home if you come with me.（= I will come home only if you come with me.） 只有你跟我一起走,我才回家.
因此,根据上面的分析,课文中的句子我们也可以把它改成Yet they could get the blood only if one of the frightened children would agree to give it.这样,句子就比较容易理解,意思也就十分清楚了：但是,只有这些受惊吓的孩子中有人自愿献血,他们才能够得到血.
二、if only
1.在if only这个短语中,中心词是从属连接词if,而副词only只是加强if的语气的,因此,if only仅仅是if的一种强化形式,不仅能表达说话人的愿望,而且能表达条件.因此,它同if一样,也能引出条件状语从句.
If only they were here now,we would be able to celebrate their wedding anniversary.如果他们现在在这里,我们就能庆祝他们的结婚纪念日了.
2.if only常常用来表达强烈的愿望或遗憾,因此,主要用在虚拟语气中,用以表达强烈的愿望或非真实条件.常被译为“但愿”、“要是……该多好啊”等.例如：
If only she could have lived a little longer.要是她能活得再长一些,那该多好啊!
3.if only从句在大多数情况下用作虚拟条件句,但是偶尔也有用在真实条件句的情况.例如：
He will succeed if only he does his best.只要他竭尽全力,他就会成功.
4.if only有时也可以写成if...only.例如：
If she would only come!但愿他能来.
三、从上面的分析,我们还可以看出only if和 if only这两个短语都可以用来引导条件从句,表示主句所需要的“条件”,但是两者有差异,主要表现在说话人的语义意图等方面.
1.only if 引起的条件状语从句,是一个对“条件”限制更严的“限制性条件状语从句”,表示“只有……(才) ；只有在……的时候；唯一的条件是……”的意思；与if引起的一般条件句相比,它有一种增强主句语势的作用.例如：
Only if the case is urgent should you call out the doctor in the middle of the night.只有患者情况紧急时,你才可以在半夜叫医生看病.
2.if only引导的条件句,通常用来表示说话人对某事所寄予的某种强烈愿望,相当于as long as.它可以独立使用,用来表示由于客观条件限制,为某事不大可能或完全不可能实现而感到惋惜或遗憾的复杂心情,常用虚拟语气.例如：
If only I were as clever as you!要是我像你一样聪明该多好啊!

as long as 与only if的用法区别
一、基本用法的差别
1.as long as 有两个意思,一是用于本义,意为“与……一样长(久)”,在否定句中,也可说成 (not) so long as；二是用于引申义,表示“只要”,用于此义时也可说成 so long as(不管是肯定句、否定句还是疑问句).如：This river is as long as that one.这条河与那条河一条长.He lived abroad as long as five years.他住在国外长达五年之久.He didn’t stay there as [so] long as she.他在那儿住得不如她久.As long as it doesn’t rain we can go.只要不下雨,我们就可以去.只要不下雨,我们就可以去.As [So] long as you need me,I’ll stay.只要你需要我,我就留下.2.only if 可视为 if 的加强说法,即其中的 only 是修饰 if 从句的,其意为“只有在……条件下”.如：I’ll tell you,but only if you don’t tell anyone else.我可以告诉你,但条件是你不能告诉其他任何人.I’ll accept the bill only if you send it to my home address.你必须把账单送到我住的地方,我才愿意偿付.
二、语气上的差别从语气上看,
only if 的语气要比as long as 强,as long as 通常只是用于提出一个条件,与if 的意思比较接近；而only if 引出的从句内容则通常暗示它是主句内容的唯一条件,含有“只有……才……”“只有在……的时候”“……唯一的条件是……”之意.比较：As long as you do your best,we’ll be happy.只要你尽力,我们就满意了.You can borrow the book as long as you keep it clean.只要你不把书弄脏,这书你就可以借.We can succeed only if everyone in the team pulls his weight.我们全队只有人人各尽所能才能取得成功.The coach stops at the principal hotels to pick up tourists,but only if they arrange this in advance.大客车到各主要的旅馆来接观光者,但条件是必须事先安排好.
三、动词搭配上的差别在许多情况下,
as long as 与 only if 均可用,只是语气有强弱之分.但是,当主句和从句的谓语动词均为短暂性动词时,通常只用 only if,而不用 as long as.如：.如：你只有请他,他才会来.误：He will come as long as you ask him.正：He will come only if you ask him.析：此句中的 only if 不能用 as long as 代替,因为动词 ask 与 come 均短暂性动词.
四、词序上的差别
两者均可引导从句置于主句之后,也可置于主句之前.但是,当only if 引导的状语从句置于主句之前时,其后的主句要用倒装语序,而且 as long as 引导的从句置于主句之前不用倒装.如：As long as it doesn’t rain we can play.只要不下雨,我们就能玩.As long as you’re happy,it doesn’t matter what you do.只要你高兴,你做什么都没关系.Only if a teacher has given permission is a student allowed to enter this room.只有得到教师的允许,学生才可以进这间屋.Only if the red light comes on is there any danger to employees.只要红灯一亮,就表示有危及职工的险情.

only if,只要,只有：That Only
Happened If 这只发生如果……
if only 表示要是……多好,只要,一种期盼,if only it look forward
if not 如果不,表条件 假设,if you not leave 如果你没离开的话
what if 假如……会怎么样 What if you could do sth 如果你可以做某事

They agreed to lend us the car only if we returned it before the weeken.
例如在这个句子中我觉得用provided和only if都可以,两者有什么区别呢,在意思和用法上


only if 的意思是只要 而provided则是可提供的.在意思上就差很远了,
同时,only if 是连词,用来连接句子,而 provided则是一个形容词,用来修饰名词的.
此处应该是天only if 而不能用provided.

你是在说if only
两者都有要是,只要的意思
if only 指之前发生的事 [要是她肯听我的话,他们就可以解决问题了.If only she'd listen to what i'm saying,I'm sure they could work it out.]
as long as 指在什么情况下,另外一件事才会发生【I can come as long as I can leave by 4.00.只要我在四点前出发,我就能来

记住了,only if的实质就等于if,only只是修饰词.从意思上讲,only if=as long as,表示“只要”,引导的是条件状语从句.但出题目时候,only if很容易放在句首,因为only修饰了状语,所以后面要部分倒装,比如Only if you work hard can you succeed.=You can succeed only if you work hard.=You can succeed as long as you work hard.
if only引导的从句,后面都是虚拟语气,有一种“如果...就好了”的感觉.

if已经是连词，无需再加一个连词that

only if用于陈述事实或必要的条件,比if所表达的语气更强烈.如果非要说需要注意什么的话,就跟if一样,主将从现.
倒是if only需要注意,有可能是虚拟语气.
eg.If only I had got it. 要是只有我得到它了该多好啊.
注意,在虚拟语气的从句中,动词be的过去时态一律用were,不用was.

如果生命可以如果,那么但愿即将到来的将会轰轰烈烈.

I wake up only if the alarm clock rings

you can only learn if you pay attention.
只有你投入精力才能学会.
only 在这里是副词哦~修辞learn.所以放在前面哦~

复句式
Only if we possess firm confidence with joint effort,we could overcome(其实survive这词儿也不错) this economy crisis.
单句式（含倒装结构）
Only if possessing strong faith with joint effort may we put up with this financial crisis.

even if 即使
as if 就好像,仿佛
if only 要是...该多好啊
例：If only I had worked harder!
要是我更加努力一点该多好啊!
only if 只有当...才
例：Only if you work hard can you succeed.
只有当你努力了你才能成功.

only 引导从句的时候放在第一位,后面的句字要完全倒装.
如果不是引导从句,就不要倒装.例如,
only 1 person attended his party.

if only: 要是...多好
Examples:
1. If only he had been here.
要是他当时在这儿就好了。
2. I dread the coming exams. If only I could have time to review my lessons.
我对即将到来的考试非常担心。如果我有时间复习该有多好啊。
3. If only I had another chance.
要是我再有一次机会就好了。
4. I am so tired. If only I can take the day off tomorrow.
太疲倦了。如果明天能不上班多好。
5. If only problems would come one at a time!
要是问题一次只发生一个该多好！
6. If only it clears up, we'll go.
只要天一放晴,我们就去。
7. If only one had an unlimited supply of money!
要是财源不断就好了！
8. She would be a very good player if only she could get it together.
她若能控制得当就能成为很好的选手.

only if:
conj. 只有当(只是在...的时候)
Examples:
1. The company will succeed only if it have sufficient backing.
只有当该公司获得足够的资助，它才会成功。
2. A compound proposition that has components joined by the word and or its symbol and is true only if both or all the components are true.
综合命题由和或其符号所连接的子句组成的复合命题，只有当所有子句为真时，该句才为真
3. I can buy the house only if a mortgage for 2000 dollars is available.
只有拿到两千美元的抵押贷款，我才买得起那栋房子。
4. Only if I get a job will I have enough money to go to school.
我只有找到了工作才有足够的钱上学。

only if 是标准的‘只有 才”的意思,用法示例:ONLY IF STUDY HARE CAN YOU GET GOOD GRADES.

if only 用于虚拟语气，表示“要是...就好了” If only one had an unlimited supply of money! 要是财源不断就好了！（与现在事实相反） only if 意思“仅仅如果”，用于引导条件状语从句。

只有……才……的句型应该是：
only……can……
例句：Only by working hard can we succeed.
只有努力,才能成功

only if (用于句首,后接从句主谓倒装)只要;只有conj.只有当(只是在 ...的时候)例句:Only if I get a job will I have enough money to go to school.我只有找到了工作才有足够的钱上学.I can buy the house only if ...

as if

一、only if
1.在only if 这个短语中,副词only是中心词,而从属连接词if则只是用来连接从句的,因此,它表示“只有……(才)；只有在……的时候,唯一的条件是……”的意思.例如：
I told him he would succeed only if he tried hard.我告诉他,只有努力才能成功.
2.only if 有时也写成only...if,表示唯一的条件,但是意思不变.例如：
I will only come home if you come with me.（= I will come home only if you come with me.） 只有你跟我一起走,我才回家.
因此,根据上面的分析,课文中的句子我们也可以把它改成Yet they could get the blood only if one of the frightened children would agree to give it.这样,句子就比较容易理解,意思也就十分清楚了：但是,只有这些受惊吓的孩子中有人自愿献血,他们才能够得到血.
二、if only
1.在if only这个短语中,中心词是从属连接词if,而副词only只是加强if的语气的,因此,if only仅仅是if的一种强化形式,不仅能表达说话人的愿望,而且能表达条件.因此,它同if一样,也能引出条件状语从句.
If only they were here now,we would be able to celebrate their wedding anniversary.如果他们现在在这里,我们就能庆祝他们的结婚纪念日了.
2.if only常常用来表达强烈的愿望或遗憾,因此,主要用在虚拟语气中,用以表达强烈的愿望或非真实条件.常被译为“但愿”、“要是……该多好啊”等.例如：
If only she could have lived a little longer.要是她能活得再长一些,那该多好啊!
3.if only从句在大多数情况下用作虚拟条件句,但是偶尔也有用在真实条件句的情况.例如：
He will succeed if only he does his best.只要他竭尽全力,他就会成功.
4.if only有时也可以写成if...only.例如：
If she would only come!但愿他能来.
三、从上面的分析,我们还可以看出only if和 if only这两个短语都可以用来引导条件从句,表示主句所需要的“条件”,但是两者有差异,主要表现在说话人的语义意图等方面.
1.only if 引起的条件状语从句,是一个对“条件”限制更严的“限制性条件状语从句”,表示“只有……(才) ；只有在……的时候；唯一的条件是……”的意思；与if引起的一般条件句相比,它有一种增强主句语势的作用.例如：
Only if the case is urgent should you call out the doctor in the middle of the night.只有患者情况紧急时,你才可以在半夜叫医生看病.
2.if only引导的条件句,通常用来表示说话人对某事所寄予的某种强烈愿望,相当于as long as.它可以独立使用,用来表示由于客观条件限制,为某事不大可能或完全不可能实现而感到惋惜或遗憾的复杂心情,常用虚拟语气.例如：
If only I were as clever as you!要是我像你一样聪明该多好啊!

因为这句话表示只有A,才有B, 说明A是B的必要条件,B是A的充分条件,所以B—>A

if only 放句首是不用倒装,但要用虚拟语气
对现在事情的虚拟用 一般过去时态
对过去事情的虚拟用 过去完成时态
对将来事情的虚拟用 could/ would/ should/might +do
only if 不用虚拟语气
only 放句首时限制if 引导的条件状语从句,主句采用半倒装

只有/只有你一直做我的家庭作业一直到学期末.
这还是一个条件状语从句结构,从句中until the end of the semester又是if从句中的时间状语.
有时候条件状语可以用来独立成句,从上下文推断主句含义.
比如If only I were rich.但愿我有钱就好了.
个人浅见.

only if表示"只有"；if only则表示"如果……就好了"。If only也可用于陈述语气。 I wake up only if the alarm clock rings. 只有闹钟响了，我才会醒。 If only the alarm clock had rung. 当时闹钟响了，就好了。 If only he comes early. 但愿他早点回来。 辨析only if 与 if only only与if这两个单词随意组合，可以组成两个意义相近，但用法不尽相同的短语only if与if only。现将它们的具体用法辨析如下： 一、only if意为“only on the condition that, as long as”，“只要；假如”。它用于陈述事实或必要的条件，比if所表达的语气更强烈。 You'll pass this course only if you study. 只要你学，你就会通过这门课。 Children may enter the club only if they are accompanied by adults. 只要孩子们有大人陪同就可以参加俱乐部。 The students at the university can take up part-time job only if it doesn't interfere with their studies. 只要不影响学业，这所大学的学生可以从事兼职工作。 二、if only则有两种含义。第一种含义与only if近似，意为“as long as”，“只要”。例如： If only it clears up, we'll go. 只要天一放晴，我们就去。 第二种则是“expressing a wish or assumption”， “但愿；如果……就好了”。它用来表达一个不可能实现的愿望或假设，句子要用虚拟语气。例如： If only she would come!要是她能来就好了！ If only you had told me you had a spare ticket for the show. 如果你告诉我，你多了一张演出票就好了。 If only you had worked with greater care!你要是工作更仔细一些该多好！ 如果有帮到您 请给予好评 如果还有问题 请重新提问哦 谢谢拉#^_^#祝您愉快

条件状语从句：
The class I teach is available only if there are enough students who will enroll for it.
only if "只有......"，引导条件状语从句，放句首时，主句部分倒装。如：
Only if you work hard, can you make great accomplishments.
你只有努力工作，才能取得大的成就。

主倒从不倒,only if中的if 引导的就是从句,所以应是后面的主句倒装!