四、借助标点识别
例4 There are altogether eleven books on the shelf. Five ________ are mine.
A. on which B. in which C. of which D. of them
【解析】选D。shelf和Five之间的句号说明第二个分句为完整的句子。但是如果把句号改为逗号，后分句则变为非限定性定语从句，应选C。
五、利用还原法：把倒装式、强调式或疑问式的题干变换为陈述句就容易了。
例5 It was ________ back home after the experiment.
A. not until midnight did he go B. until midnight that he didn’t go
C. not until midnight that he went D. until midnight when he didn’t go
【解析】将强调句还原为陈述语序：He didn’t go back home after the experiment until midnight. 当被强调的是not…until句型中的until引导的时间状语时，要将not放在until的前面。基本句式为It is / was + not until…that…。故答案为C。
