1.中文：我要是你，我不会那么做。

　　(误)I shouldn't do that if I was you.

　　(正)I shouldn't do that if I were you.(表示与现在事实相反的虚拟语气不能用was，只能用were.)

　　2.中文：要是我父亲现在在这里，他会告诉我该做什么。

　　(误)If my father were here now， he will tell me what to do.

　　(正)If my father were here now， he would tell me what to do.(表示与现在事实相反的虚拟语气中，主句的助动词只能用would，might等过去时。)

　　3.中文：要是我知道她的电话号码，我就会给她打电话了。

　　(误)If I knew her telephone number， I would have called her.

　　(正)If I had known her telephone number， I would have called her.(表示与过去事实相反的虚拟语气中，条件从句的动词要用过去完成时。)

　　4.中文：要是昨天没下雨她也许会来。

　　(误)If it had not rained yesterday， he might come.

　　(正)If it had not rained yesterday， he might have come.(表示与过去事实相反的虚拟语气中，主句的动词要用助动词的过去时might，could等+HAVE+过去分词。)