1、主將從現(xiàn) (主句為一般將來(lái)時(shí),從句為一般現(xiàn)在時(shí)); eg:If it rains(從句) ,I will stay at home(主句). =I will stay at home if it rains.
2、主句含有情態(tài)動(dòng)詞 (must、may、can etc.)從句為一般現(xiàn)在時(shí); eg:If you drive too fast ,you may have an accident. =You may have an accident if you drive too fast.
3、主句為祈使句,從句要用一般現(xiàn)在時(shí)態(tài); eg:Don't play computer games if you don't finish your homework.