改成被动语态,最关键的是要找出主语和宾语,
1 we found some jewls in a box
Some jewls in a box was found by us.
2 the teacher is keeping the pupils at school for a revision
The pupils are being kept at school for a revision by teather.
3 James has left a parcel for you
A pancel has been left for you by James.
4 you must finish the article before Friday
The article must be finished before Friday.
……
你应该已经看出来怎么做了吧,加油!