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.

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。

We played well, but I felt the team were            by one member, who didn’t try his best on the court.

let down

turned down

picked up

cheered up

考查动词短语辨析。句意：我们打得很好，但我觉得有一个队员在场上没有尽最大努力，让整个球队失望了。A. let down 使失望，放下；B. turned down 拒绝，调小；C. picked up捡起，接；D. cheered up使兴奋，振奋。结合句意可知，“有一个队员在场上没有尽最大努力”，所以“我们”感到失望。故选A项。

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。