The boy on the playground ____ be Tom, because he saw him in the library just now.

Many social workers went to Ya’an to ______ clean water and food to local people to reduce their pain from the earthquake.

Have you returned the book to the library ____?         --- Yes, I have ____ returned it.

The air in Dongying is much worse than that in many other cities. We must do       to protect our environment. 

The old lady donated much money to the poor students. ______she is not rich．