过去完成时练习题及答案

1. When I arrived at the station, the train _____ already.A. leftB. has leftC. had leftD. leaves答案：C解析：句子中“arrived”是过去时，而“left”的动作发生在“arrived”之前，所以使用过去完成时。2. By the time he came back, we _____ the work for hours.