______it rain tomorrow,we would have to put off the visit to the Yangpu Brid

_______ it rain tomorrow，we would have to put off the visit to Yangpu Bridge.
A. Were B. Should C. Would D. Will

b
原句应是If it should rain tomorrow,we would have to put off the visit to the Yangpu Bridge.
倒装后为Should it rain tomorrow,we would have to put off the visit to the Yangpu Bridge.
所以B
虚拟语气倒装 仅should were had 提前，其他不动。were to 与should等效用于对将来的虚拟。were，had分别表对现在、过去的虚拟。具体见虚拟语气用法及虚拟语气倒装。

B

A 虚拟语气

答案选 B. Should 这是虚拟语气的用法 原句应是If it should rain tomorrow,we would have to put off the visit to the Yangpu Bridge. 倒装后为Should it rain tomorrow,we would have to put off the visit to the Yangpu Bridge. 当虚拟条件句的谓语动词含有were, should, had时，if可以省略，这时条件从句要用倒装语序，即把were, should, had等词置于句首，这种多用于书面语。 eg： Should he agree to go there, we would send him there. 　　 要是他答应去的话，我们就派他去。