用所给单词的适当形式填空。(24分)
（1）Mary ________(have)a beautiful doll.
（2）She ________(not have)PE classes on Tuesdays.
（3）Do you often ________(read)in the library?
（4）We have two science ________(class)a week.
（5）How many ________(boy)are there in your class?
（6）We can ________(observe)things in the science class.