should倒装表示虚拟语气，比if 虚拟语气要弱一些，相当于中文万一的概念。
if it were to rain tomorrow ，we would cancel the picnic on weekend
也可以表示万一明天下雨，---
if it should rain tomorrow ，we would cancel the picnic on weekend
经过倒装，最后成为
should it rain tomorrow ，【we would】 cancel the picnic on weekend.
内容全部来源于网络收集，如有侵权，请联系网站删除：QQ：24596024