题目内容：

would join them in the dress-up party __.A.if they invite B.should they invite us...
would join them in the dress-up party __.
A.if they invite B.should they invite us.为什么选B不选A?为什么把should提前可以省略if?

优质解答

invite是及物动词,要加直接宾语,所以A不对.
B采用的是虚拟语气,倒装句式.
虚拟条件句的从句部分含有were,should,或had时,可省略if,再把were,should或had 移到从句的句首,实行倒装.