题目内容：

根据句意和汉语注释，写出单词的适当形式

1.Amy is afraid of making__(演讲) in front of many people.

2.Columbus__(发现）America in 1492.

3.In the library we should read in___(安静).

4.Danny is in low___（精神）. What has happened to him?

5.Air pollution has been a___（国家的）problem in China at present.