三个英语基础知识问题,燃眉之急!

三个英语基础知识问题,燃眉之急!
③Curious to know what the bag [contained] ,Little Johnny [felt] it ,because of which his father blamed
him.
这里的[contained]为什么不是主动形式?
[felt]是感觉的意思,
④The steel works in which David has worked for five years [has been supplying] us with raw material in
large quantities in the past two years.
[has been supplying] 中的has要改成have吧?works不是复数么?干嘛要用第三人称单数?
⑤let sb do sth.
这里为什么能用do呢?不是应该用非谓语结构吗?