What ___ a knife ______ (make) of? 

The old man is ill. He ______ (must send) to the hospital.

That play ________(put) on again sometime next month.

The students _____ often _____(tell) to take care of their desks and chairs.

We clean the classroom every day. （变为被动语态）

  The classroom ____  ____ every day.

They have sold out the light green dresses. （变为被动语态）

  The light green dresses ____  _____  ____ out.

Did he break the window yesterday? （变为被动语态）

____ the window ___  ____  ___  yesterday?

They use knives for cutting things. （变为被动语态）

  Knives ___ ___ for cutting things.

We must water the flowers every day. （变为被动语态）

  The flowers must ___ ___ (by us) every day.