麻烦各位：这道定语从句怎么做啊：I will never forget the days ________i spent in Xi'an

spend是及物动词，后面要带宾语才能构成完整的句子，所以用which或者that来引导．因为是充当宾语成分，所以也可以不填

1.when.在从句中不充当成分,只起引导从句的作用.
2.which.which在定语从句中可以充当主语,宾语,表语.

spent后面缺少宾语,所以要用which充当从句的宾语.
应该是which

when