C.explosion D.standard

答案　B

解析　set the ceiling at为固定短语，意为"设置上限(为)"。ceiling最高限度，上限，天花板。故选B。

6.It might have your notice but I am very busy at the moment.

A.quit B.neglected

C.escaped D.denied

答案　C

解析　句意为：你可能没有注意到，但我现在很忙。quit离开，放弃；neglect忽视；escape逃脱，逃避，被忽视；deny否认。故选C。

7.He is a newcomer in the team，but I have the that I've seen that man before.

A.function B.impression

答案　B

解析　句意为：他是新加入我们队的，但是我有印象以前见过他。impression印象。故选B。

8.He hurried home，never once looking back to see if he .(2017·江苏，27)

A.was being followed

B.was following

C.had been followed

D.followed

答案　A

解析　句意为：他匆忙回家了，一次也没有回头看看他是否正被跟踪。这里if引导的宾语从句用过去进行时表示过去某一时刻(hurried home)正在进行的动作。又因he与follow之间是被动关系，故用被动语态。综上可知选A项。

9.With the word PM 2.5 appearing in media reports，people pay greater attention to it and seek health tips for smoggy days.

A.immediately B.consequently

C.permanently D.constantly

答案　D

解析　immediately立刻，马上；consequently所以，因此；permanently永久性地； constantly连续不断地。句意为：随着词汇"PM2.5"不断地出现在媒体的报道中，人们更加关注雾霾并寻求在雾霾天保持健康的建议。