If there are         trees, the air in our city will be         cleaner.

 —Which is _______, the sun, the moon or the earth?—Of course the sun. 

____________ the teachers is about 300 in our school and it is becoming_____________.

-What do you think of the traffic in our city?-lt's    than it used to be, but there's still a long way to go.

--- How many English words should I remember, Mr. Black?--- ______, the better, of course.