If you work hard like this, you will           sooner or later.

give out

break up

break down

fall down

考查动词短语。句意：如果你继续这样辛苦工作的话，你迟早垮掉。A.give out分发 ；B.break up打碎；C.break down垮掉；D.fall down 跌倒。根据句意可知break down符合语境。故选C项。

Only then_______ how much damage had been caused.

she realized

she had realized

had she realized

did she realize

“only＋状语”位于句首，整个句子用不完全倒装．此外，由then可确定用过去时态．

The salesman scolded the girl caught         and let her off.

to have stolen

to be stealing

to steal

stealing

考查非谓语动词。句意：这个销售员责备了被抓住正在偷东西的女孩，然后，让她走了。分析句子结构，caught是过去分词作定语，修饰前面的名词 the girl,"女孩"和"偷东西"之间是主动关系，用现在分词作宾语补足语，构成catch sb doing sth结构。意为抓住某人正在做某事。故选D项。

It was fortunate that Jack narrowly escaped             in a traffic accident last month.

killing

being killed

to be killed

 to kill

考查非谓语动词。句意：杰克上个月在交通事故中死里逃生，真是幸运。固定表达escape doing sth.逃离做某事。此处Jack与kill之间是被动关系，应该使用动名词的被动语态，用being killed。故选B项。

______about wild plants that they decided to make a trip to Madagascar for further research.

So curious the couple was

So curious were the couple

How curious the couple were

The couple was such curious

---Shall I tell Jhon about it?

---No, you            . I've told him already.

needn't

wouldn't

mustn't

shouldn't

考查情态动词。句意：---要我告诉约翰这件事情吗？--不，不必了，我已经告诉他了。A.needn't不必；B. wouldn't不会；C. musn't禁止，不允许；D. shouldn't 不应该。根据“I've told him already”，可知这里是“不必要”。故选A项。

used to

used to be

used to do

was used to

考查词组和省略式，used to do“过去常常’,be used to do “被用来做”，句意是：--你现在是志愿者吗？--不但我过去是，去年我为市运动会工作。可以排除D项，因为这是省略句，完整的是I used to be a volunteer。英语中如果不定式的部分是重复上文可以省略to后面的内容，但是如果to后面是be动词或助动词have，就不省略。选B。