Question

Turn from active into passive.
1)They must pay their phone bill.
2)You should lock the front door.
3)You must sign these papers.
4)He has to deliver the parcel
5)You ought to put your toys away
6)We must protect the environment

Answer 1

1) Their phone bill must be paid.
2) The front door should be locked by you.
3) These papers must be signed by you.
4) The parcel has to be delivered by him.
5) Your toys ought to be put away.
6) The environment must be protected by us.

Answer 2

1)Their phone bill must be paid. 
2)The front door should be locked. 
3)These papers must be signed by you. 
4)The parcel has to be delivered by him.
5)Your toys ought to be put away.
6)The environment must be protected.