横线上为什么填 which?A.And B.that C.which D.不填

题目

横线上为什么填 which?A.And B.that C.which D.不填
But if you consider American history,it's easier to see where this pattern of behavior comes from.In the pioneer days,if you acted too reserved and formal,no one would have any reason to help you if you got introuble (______ there was plenty of in the pioneer days).

答案

因为 there was plenty of in the pioneer days是定语从句.
横线处需要填引导定从的关系代词,这个关系代词指代trouble,且在定从中作介词 of 的宾语.
即:...there was plenty of (trouble) in the pioneer days.
因此用which.
that也可引导定从,作宾语,但不能作介宾.
虽然关系代词与介词分开了,好像that也可,但与which相比,which是最佳答案.