题目内容：

 

1.The little girl broke the window __________.(意外地)

2.He got bad grades in the math exam. His parents were __________him. (担心)

3.Olympic Games ________every four years. (发生)

4.He looks up to those ________.(民族英雄)

5.________is the hottest topic all over the world at present. (环境保护)