问题补充:
单选题Iarrivedhomeatmidnight,_______myparentshadbeenwaitingfornearlythreehours.A.at that timeB.by that timeC.at which timeD.by which time
答案:
D解析这题考查介词和非限制性定语从句,从句式结构看这是非限制性定语从句,又根据从句的时态:过去完成时,可以判断是by,所以填by which time。选D。句意是:我午夜到家,到那时为止我父母已经等了近3小时了。