1、We had learned "six" pop songs by the end of last week.
(How many) pop songs had you learned by the end of last week?
截止到上周末你们学了几首流行歌曲?
2、He went to the hospital"to have a checkup on eyesight.“
(Why did) he go to the hospital?
他为什么去医院?
3、He lost"the key of his bike" on his way to the lecture.
(What) did he (lose) on his way to the lecture?
他在去听讲座的路上丢了什么?