`Answer :` 

`1.` The trees shouldn't be cut.

`2.` The result will be known by him in a week.

`3.` French will be started by our class next term.

`4.` Bikes must not be left in the hall by students.

`5.`The bill has to be paid by him.

`6.`The letter ought to be sent at once by you.

`7.` The truth will be told to you by someone.

`8.` They will be met by me at midnight in the middle of the wood.

`9.` The problem will be solved by Nam soon.

`10.` They will be helped by that kind woman.

$----------------------$

`->` Bị động thì TLĐ : S `+` will `+` be `+` V`3`/ed `+` ( by `+` O )

`-` Bị động động từ khuyết thiếu : 

`-` S `+` ĐTKT `+` be `+` V`3`/ed

`-` Should `+` V `→` Should `+` be `+` V`3`/V-ed.

`-` Ought to `+` V `→` Ought to `+` be `+` V`3`/V-ed.

`-` Must `+` V `→` Must `+` be `+` V`3`/V-ed.

`-` Have/has to `+` V `→` Have/has to `+` be `+` V`3`/V-ed