题目内容：

根据句意和汉语注释，写出单词的正确形式。

1.There was a large family photo ____________（悬挂）on the wall.

2.The population in this city has ___________（增加）from 1.2 billion to 1.8 billion.

3.Three ___________（四分之一）of the boys in our class like ball games.

4.I carelessly dropped some paint on the __________（表面）of the desk while painting.