he once studied at one of the most famous universities( )he doesn't want identified为什么是which不是where

he once studied at one of the most famous universities( )he doesn't want identified为什么是which不是where he was up at once most adults once studied He was fired at once.at once怎么翻译? -----he---- at this school last team A.Did,studyB.Has,studied C.Was,studyD.Did,studied Tom__in China now.He calls his parents once a week.A.is studying B.will study C.has studied D.studied 改错1.He studied very hard .and at the end he passed the exam. The school where he once studied is very famous.为什么这里用where 如果 改成The school which he once studied in is very famous.就变成了用which! 英语小小问题Mark was a student at this university from 1990 to 1995,during which time he studied hard.为什么during后面用which?After the war,a new school building was put up where there had once been a theatre.这里 where there had once b Tom ____ in china noe.he calls his parents once a week.a,is studyingb,will studiedc,has studiedd,studied at once at once 【英语】He suggested that the new book____(print)at once The man is seriously ill.He needs ----------- (operate)at once. He was made___(leave) the room at once 他必须马上改变生活方式.英文he must [ ] at once. 为什么用since?my bother studied at the high school since he joined the army he studied hard,aiming at passing the exam.为什么aim要加ing?请详解.