①煤的燃烧  ②工业废气任意排放  ③燃放鞭炮  ④飞机、汽车尾气的排放．

根据对话情景，在画线处填上适当的单词，使对话完整通顺。
A: Hello!
B: Hello! ____  is Bob. May I speak to Peter please?
A: Speaking.
B: Hi, Peter. Can you help me?
A: Certainly. ____ the matter?
B: My model ship doesn't____ . Can you mend (修理) it?
A: Yes. But I am busy today. What about Sunday morning?
B: Sorry, I can't hear you. The line is ____.
A: How about half ____  eight on Sunday morning?B: OK. Thanks a lot. See you then.
A: See you.

Smoking is bad for your health. You'd better _______.