(1)介词或介词短语。如but for,but that,without,in case of, under more favorable condition等。
(2)连词。如so that, unless, in case, supposing,lest, provided(倘若……),for fear that(唯恐),in orderthat, on condition that, if only(要是……就好了)等。
注意:lest, for fear that和in case引起的从句中谓语动词多用should+动词原形,但也可以不用虚拟语气,而用动词的陈述语气形式。例如:The foreign teacher spokeslowly in case we misunderstood him这位外籍教师说得很慢以免我们误解。