Small sailboats can easily turn over in the water ________.

if not managed carefully

if are not managed carefully

unless not managed carefully

unless are not managed carefully

If you don't understand something, you may resrarch, study, and talk to other people          you figure it out.

because

though

until

since

考查连词。句意：如果遇到不懂的东西，你可以搜索、研究，和别人交流直到弄明白。A. 因为； B. 尽管；C.until直到；D.since自从，因为。根据句意可知，until符合语境。故选C项。

Tom looks so pale today. He ______ ill.

must be

had to be

should be

shall be

[翻译]汤姆看起来脸色不好，他一定生病了。[解析] A 试题解析：情态动词must表示推测。题目中表示肯定的推测。

Don't forget            the letter for me when you pass  by the post office.

post

to post

posted

posting

考查不定式作宾语。句意：你经过邮局时别忘了替我寄这封信。forget to do sth忘记要做某事；forget doing sth 忘记做过某事。根据句意表示事情已经发生。故选B项。

Great amounts of water            poured into the river from the factories two years ago.

was

were

has been

have been

考查时态和主谓一致。句意：两年前，工厂将大量废水排入河中。根据two years ago 可知，句子使用一般过去时。....amounts of修饰不可数名词作主语时，谓语动词用复数形式，即谓语动词与amounts保持数的一致。故选B项。

The wise parents can tell whether their children are telling the truth         they listen to their excuses to wrong deeds.

the first time

every time

for the first time

for every time

考查时间状语从句。句意：每次听孩子对错误行为的辩解，聪明的父母都能分辨出他们是否在说真话。此处引导时间状语从句，表示“每一次” 应用every time。the first time表示“第一次”，与语境不符；for the first time作时间状语，不可引导从句；没有for every time 的表达方式。故选B项。

I thought we'd be late for the concert,           we ended up getting there ahead of time.

but

or

so

for

考查连词。句意：我以为我们音乐会迟到了，但是我们提前到达了那里。but 但是；or 或者；so 因此；for因为；两个分句在意义上bu是转折关系，故用but。故选A项。