Many trees and flowers ________ in our city every year.

China has offered much help to Japan since it ______ by the earthquake and tsunami（海啸）.

 —Do you want to see the painting exhibition at the weekend?—I won’t see it unless I __________.

---Mum, can I go to the zoo with Linda? ---When your homework _______, you can. 

Stamps are usually used _____letters.