要根据句中所表述的意义以及某些特定的信息词来判断此时需要采用的形式。常用词或短语有：without, but for, or, otherwise等。

　　But for her help, they couldn't have run over the mountain in such a short time.

　　要不是她的帮助，他们不会在那么短的时间内翻过那座山。

　　I was ill that day.Otherwise, I would have taken part in the sports meeting.

　　我那天病了。否则，我就参加运动会了。

　　He must have been there, or he never could know the place so well.

　　他一定去过那儿，否则他决不会如此了解那个地方。

　　　[即时演练2]

　　(1)单句语法填空

　　①(江苏高考改编)Many of the things we now benefit from would not be around but_for Thomas Edison.

　　②(重庆高考改编)Without his wartime experiences, Hemingway wouldn't_have_written (not write) his famous novel AFarewelltoArms.

　　③(安徽高考改编)It is lucky we booked a room, or we would_have (have) nowhere to stay now.

　　(2)完成句子

　　④要是没有你的帮助，我们是不会成功的。

　　But for your help, we couldn't_have_succeeded.

　　⑤她感到不舒服，不然她不会那么早离开会场。

　　She wasn't feeling well.Otherwise she wouldn't_have_left the meeting so early.

语法点三 虚拟语气在名词性从句中的应用 　　1.在宾语从句中的应用

　　(1)wish后的宾语从句。

时间 谓语动词的虚拟形式 对现在的虚拟 一般过去时(be用were) 对将来的虚拟 would/could/might＋动词原形 对过去的虚拟 过去完成时 　　I wish (that) I were a bird and could fly freely in the sky.

　　我希望我是一只小鸟能在天空自由飞翔。

　　I wish (that) I had met that film star yesterday.

　　我希望昨天见到那个影星了。

　　　[即时演练3]

　单句语法填空