While he was going shopping,I slept还是was sleeping,为什么?那如果是while he was taking a shower ,the UFO landed.这里的while可以换成when吗

While He Yan was at the doctor's.I was going…为什么是doctor's while he yan was at the doctor's,I was going to the class这里为什么不用WHEN While he was e() While He Yan was at the doctor's,I was going to the class.while引导的从句是用进行时,这里用的却是过去时? He met many problems__he was going over his lessons 为何用while while不是前后都要进行时么 关于while he yan was at the doctor's. l was going to the class英语短文 悬赏分：20 | 提问时间：2007-新目标英语八年级下unit2 self check 2作文怎么写 While he was going shopping,I slept还是was sleeping,为什么?那如果是while he was taking a shower ,the UFO landed.这里的while可以换成when吗 ______Sarah was at the barber's,I was going to class.答案是while,为什么when不可以 while he was studing为什么要was But while he was going across the lake in a boat,his bag fell into the water. He met many problems__he was going over his lessons?A.before B.as soon as C.since D.while He met many problems ____he was going over his lesson A.before B.as soon as C.since D.while he was going to start the car when/while a gunman jumped up from the back seat.选择的原因 The boy's book d_____ on the ground while he was running.填空注意时态 While you were at the __,I was going to schoolA doctor Bdoctors C doctor's Ddicits'应选什么? 初二英语（用when或while填空)1.______ Margo was talking on the phone,her sister walked in.2.______ we visited the school,the children were playing games.3.______ Sarah was at the barber's,I was going to class.4.______ I saw Carlos,he was the thought of going back home was ______kept him happy while he was working aboard 这里为什么不能用WHAT 只能用THAT The thought of going back home was all that kept him happy while he was work.先行词是什么?that能不能用which?