把下列各句改为被动语态。 1. We clean our classroom every day. Our classroom _____ by us every day. 2. They produce silk in Suzhou. Silk _____ in Suzhou. 3. They speak English in class. English _____ in class. 4. He teaches us ten words every class. Ten words _____ to us _____ every class. 5. We use keys for opening the door. Keys _____ opening the door.