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+