是考祈使句还是非谓语动词请看下面这道题，是考查祈使句还是考查非谓语动词：If they don’t understand it the first time, _________ over it again until they do. A. going B. to go C. gone D. go【分析】此题正确答案选D，其余几项均有可能被误选。空格前 if 引导的是一个条件状语从句，而在空格处无论是填A、B或C，它都是一个非谓语动词短语，而不是一个句子，这样一来，整个句子没有主句，从而导致结构不完整。若选D，则 go over it again until they do 则是一个句子(祈使句)，在此用作主语。又如：(1) If he likes to eat it, _________ him some more.A. giveB. giving C. givenD. to give(2) If anyone calls, _________ them I’m not at home.A. tellB. tellingC. toldD. to tell(3) When your mother comes back, _________ her to come to school at once.A. askB. askingC. askedD. to ask(4) While the baby is sleeping, _________ your work as soon as possible. A. finishB. finishingC. finishedD. to finish答案均选A，空格前分别为 if, when, while 引导的状语从句，空格处填动词原形，构成祈使句，用作句子主语。

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