when did you come here

选A,when did you come here? 是一个过去式,你什么时候来这儿的?是说你过去的某个时间点来这儿的,回答也要用过去式,two years ago,两年前,完整的回答是I came here two years ago。如果问题是how many years have you come here? 你来这儿几年了?是说你来这而几年大的这个时间段,回答,for two years,完整的回答,I have come here for two years。