1.it was his doctor who advised that he have a holiday away from the city.
因为这是he should have ...的简称,这里省略should了.这是很典型的英语句型.
2 it is essential that all these figures_twice.
这里不能选A,而应选B：be checked,即all these figures (should) be checked twice.同理.
3.这取决与前面有否已有动词.如 He was killed.
He got killed.
相信帮您解决了难题.不明白的再问哟,请及时采纳.那像第一题，主语是he，have在一般句式里应该用has，但在虚拟语气里用should+动原是不是也要把has变成have太对了！看来你掌握了诀窍。1的选项是A. have。 老实说，有些老师都不懂这个句型呢！