() it rain tomorrow,we would have to put off the vist to the Yangpu Bridge {A,Were B,Should}

题目

() it rain tomorrow,we would have to put off the vist to the Yangpu Bridge {A,Were B,Should}
我的书上只给了B答案

答案

本句是虚拟语气,条件句省略了IF,做了倒装,
虚拟语气表示将来完成的情况,条件句只能用SHOULD,从句用WOULD +现在完成时