用所给单词的适当形式填空

1. It's seven o'clock. Let's start _____(have) dinner.

2. I met an old friend while _____(walk) on the street.

3. It's too _____(noise) here. Let's go somewhere quiet.

4. It's rude _____(stick) your chopsticks into your food.

5. Who is _____(young) student in your class?

（）是指为维护人居环境与人体健康的基本需要，必须严格执行的最低环境管理限值。

A.生态功能保障基线

B.生态质量保障底线

C.生态空间开发上限

D.环境质量安全底线