第2个回答 2011-11-05
①与过去事实相反,在从句中用过去完成时形式表示。
②与现在事实相反,在从句中用一般过去时形式表示。
③与将来事实可能相反,在从句中用动词过去式,should +动词原形,或were to + 动词原形表示。例:
⑴、If I had come her yesterday, I would have seen him.
⑵、If I were a teacher, I would be strict with my students.
⑶、If it should snow tomorrow, they couldn't go out.
4、注意事项
①if条件句中如有were, should, had,可以省去if,并使用倒装语序。
②在现代英语中if条件状与从句中的谓语动词如果是be其过去形式一般用were。