you can not imagine how much we respect Prof

you can not imagine how much we respect Profyou can not imagine how much we respect Professor Johnson now,__we used to laugh at so muchA.who B.which C.where D.when答案是C我想问一下who为什么不能选,语法上who和whom都可以做宾语代指人为什么答案不能选A还有一个问题,Samuel survived when the car __he was a passenger in turned off the road and hit a treeA.where B.that C.as D.why答案选择BB和C都可以代指物是不是as一般都是用在非限制性定语从句