Though ____ the dangers of smoking to their health, smokers still find it hard to give up smoking.

aware of

are aware of

be aware of

考查状语从句的省略：句意：虽然很多经常吸烟的人已经意识到抽烟对他们健康造成了很严重的后果，但是他们仍然发现很难戒烟。Though引导的让步状语从句是省略句，完整的句子是：though smokers are aware of the dangers of smoking to their health。当主从句的主语一致的时候，可以省略从句的主语和be动词，选B

--- I'm afraid I can't complete the marathon next week.

---              ! You have been practicing a lot.

No problem

Go ahead

Cheer up

Good luck

考查交际用语。句意：---恐怕我下周不能完成马拉松比赛。---振作起来！你一直一直在不断练习。A.No problem没问题；B. Go  ahead请干吧；请便吧；C.Cheer up高兴起来；振作起来；D. Good luck祝您好运。由下文可知说话人担心，完不成马拉松比赛，由“你一直不断练习”可推断表示鼓励“振作起来”。故选C项。

It’s his brother ______ never been to Australia. You’d better take him with you.

that is

who is

that have 　

 who has

句意：就是他的弟弟从没去过澳大利亚。你最好带他和你去。根据句意及题干分析此题是考查强调句型，因为强调的是his brother，是人，所以用who引导是现在完成时态，故选D。

When it comes to modern communication, network safety is always a major          . 

concern

advantage

opportunity

solution

考查名词辨析。句意：当涉及现代通信，网络安全一直是一个主要令人担忧的问题。A. concern关心，令人担忧的事实或情况；B. advantage 优势；C. opportunity 机会；D.solution解决方案。网络安全一直是现代通信的个主要令人担忧的问题。故选A项。

It was not until 1920 ___ regular radio broadcasts began.

when

which

that

since

此题考查强调句。句意为：直到1920年，常规的电台才开始。这句话把it is/was和that去掉后，仍是完整的一句话，因此我们可以知道这是一个强调句，而且是对not...until“直到...才”的强调。结构是：it is/was+not until+其他成分。故选:C.

All we need          a piece of advice on how we can improve our time management.

are

is

were

was

考查be动词和时态。句意：我们需要的只是一条关于如何改进时间管理的建议。分析句子可知，说明一般情况应该用一般现在时，这句话的主语是All we need, 所以为主语从句，当主语从句作主语时，谓语动词用单数，所以用is。故选B项。