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。

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_____you can finish the exam in two hours.

does believe

do believe

did believed

do believed

句意：---我确实相信两个小时内能完成考试。这里用来强调，在谓语动词前加助动词do表示强调。句子的主语是第一人称，所以位于动词不能用单数，故排除A；did后用动词原形；do后用动词原形，故选B。

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 drink a cup of coffee           ; but usually I take tea.

frequently

often

constantly

occasionally

考查副词词义辨析。句意：我偶尔喝一杯咖啡，但我通常喝茶。A. frequently频繁地；B.often经常地；C.constantly连续不断地；D.occasionally偶尔地。but 表转折关系；根据后半句的usually,前面用occasionally,与usually意思相对。故选D项。