He doubted whether she would be _____to the task,

这是《老人与海》里面的一句话,I know （that）you did not leave me because you doubted.
you doubted不是you leave me的原因,翻译成符合汉语表达的方式就可以了.
此类名著有名家明议,按照他们的翻译去理解.

only! literacy and old-fashioned. Be careful to use it
补充：大哥你好懒,查查字典就知道了,but还有一个现在不常用的意思就是only,just,正如我所说的,它是文学化,下面是朗文字典的原文：
especially lit;only,just:只不过,仅仅,刚刚；He is still but a child,它只是个孩子；we can but try 我们只能试试……
如果你喜欢看上了年代的英文书,你会发现那些喜欢咬文嚼字的文人对它的情有独钟……
你说的这句话意思很简单,那就是：她怀疑她是否能让她的话变得有仅仅是可信一点；
很显然其他两位的解释是很牵强的；所以一本好字典是远胜百度的.我不敢说这里的人都是半桶水,但是起码他们的平均水平应该在美国小学毕业生之下,所以真正入了门的英语学习者应该向native speakes求助,你可以在google很容易找到这样的论坛!
当然百度的唯一用途是可以做中英翻译,不是因为这些人英文很好,实在是因为真正学中文的外国人太少了!
祝好运

in your last mail you doubted （if) it (is) useful to go to college

I know you did not leave me because you doubted.
译文：我知道你不是因为没把握才离开我的.
原段是
No,You're with a lucky boat.Stay with them.But remember I went eighty-four days without fish.Stay with them.I know you did not leave me because you doubted."I remember," the old man said."I know you did not leave me because you doubted.
那也是必然的,你交上了一条走运的船,虽然我很相信你,但是我也曾经八十四天没有走好运了,就在这呆着吧.“我记得,”老人说.“我知道你不是因为没把握才离开我的.”
摘自【美】海明威,《the old man and the sea》,译林出版社,P.2

1 that 我从未怀疑过你成功地创造了新的世界纪录.
There is no doubt that 固定短语可以试情况而改动 一般doubt后面都是that
2 one 想买个一样的
it this that 都是指题目中 you 的那个 而one能表示打算新买一个
3 So it is　牵扯的很多 比如语法和习惯用语什么的 楼主背下来好了 下次还用这个比较准 天气的话 一般都用It is
奥 看到最后才看到有答案orz

D

怀疑就是怀疑它是对是错啊,whether就是是否的意思,而用that的话就是怀疑它是真的……读起来没觉得不顺嘛……讲话就讲一步到位嘛

1.C是正确答案.
2.在否定句和疑问句中,doubt后面接that引导的宾语从句.例如：I've never doubted that you love me.
3.在肯定句中,doubt 后面一般接whether 或if 引导的宾语从句.例如：I doubt whether they can swim across the river.

She doubted whether he had any intention of marrying her.
她怀疑他是否有任何娶她的打算.
any：形容词,【任何的】,修饰后面名词【intention】.
是短语have an/no/ any /the intention to do /of doing sth的常见搭配之一.
祝你开心如意!

Dear David,
In your last mail you doubted that(改whether) it is useful to go to college.But I believe going to college will benefit me(改you) in several ways.Firstly,it will further your education and develops(改develop) your competence.General(改Generally) speaking,higher education makes a person wiser,thus making it more likely for you to live a happier life.Secondly,it is (加a) good place for you to make friends.You can build (加up) your self-confidence so(改as) well as independence,and stand on your own feet through learned(改learning) from your friends.Lastly,the training in your area of study improves your skill(改skills) and helps you progress much faster in the future career.So,to(去掉to) work hard to be admitted into a good college ,and you will earn yourselves(yourself) a bright future.