By now, more than 100 photos ________ back to the earth by C

到现在为止,现在完成时态
确定

has sent

Be attached to
“喜爱；附属于”
就用attached啊,你自己都写对了噢

y now 使用现在完成时,by now是说至今为止,事情已经……,动作是从过去持续到现在,其实还有可能会持续到未来,所以用现在完成时.而如果动作从过去的某一个时间开始,只是持续到之前的一个时间,可以是一分钟之前,也可以是很久很久之前,那个动作已经结束了,没有持续到现在,这时才用过去完成时.比如by the year of 2008这就得用过去完成时啦!

Earth tone colors are in for now,so consider this when you buy make-up.
现在很流行褐土色,你买化妆品的时候可以考虑一下.
All skepticism should by now have vanished所有怀疑在那时全消除了

y far adv
用于强调,翻译时可译为：“到目前为止”.
可修饰形容词或副词的比较级和最高级,通常置于其后,但是若比较级或最高级前有冠词,则可置于其前或其后.如：She is by far the best executive in the company.她目前是公司中最为优秀的决策人 ；She ran fastest by far.她跑得最最快.
by now adv “到现在,至今”的意思,叙述中表示可涉及的时间.例句：
They must have arrived by now.
现在他们肯定已到了.

这句回答的话里面 我们要先分析一下句子的成分
首先先可以把句子补充完整：
It must be clear that who is winning by now.
谓语是情态动词+系动词must be
时间状语是by now表示到现在为止
系动词后的表语是clear
that who is wining这个部分是是表语补足语从句
所以从语法的角度很清楚
by now在这句话里面 不是跟现在进行时对应的

这题选A:is winning
原句还原是：It must be clear to find out who is winning at the moment（by now）
by now 可用于多种时态,要根据语境具体分析哦.
By now the power of the Roman Empire was on the wane.
到这时,罗马帝国已日益衰败.
By now,putting satellites in orbit is old hat to space scientists.
现在,对航天科学家来说,把卫星送入轨道已不是一桩新鲜事了.
By now she is redoing problems — how do I get characters into a room — dozens and dozens of times.
到目前为止,她正在无数次地重复解决问题,我该怎么把一个个字母填入一个空位.
By now,all good designers and developers realize the importance of usability for their work.现在,比较牛的设计师和开发者都认识到了可用性在他们工作中的重要性.
Oh,and they go to Buckingham Palace to receive medals from the Queen and,by now,more or less accept it as their due.对了,他们还去了白金汉宫接受了女王的勋章,并且直到现在,或多或少地还是人们接受他们的原因.
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如对回答满意,

until now意思是一直到现在,一直在发生,迄今为止
by now意思是截止到现在,开始发生
举两个例子
By now you should have the feel for this
Until now i have always lived alone

看情况而定.
常用完成时.也可以用一般时,过去时,将来完成时.
Her secret remains untold by now.
How many people have accessed your homepage by now
By now the power of the Roman Empire was on the wane.
By now,a rocket will have set off on its35 million mile trip to Mars and scientists must be waiting anxiously for the results.

D
首先,by now表明要用完成时,其次主语是construction 不可数名词,谓语动词用has不用have,再次,铁路线被修建,被动句,故选择 has been completed

因为比赛是正在进行,还没有完.而赛场上的形式已经很明显,哪个队会赢.
所以用现在进行时

可以.by now i'm still going to the school.像这样的.

A 他直到现在也没出现,现在完成式,表示过去状态持续到现在而且可能继续持续下去.