补全对话。从方框中选出适当的句子补全对话。
A: Lucy, why are you going out   ?
B: That’s the sound of a truck collecting rubbish.
A: Do you mean you have to take the rubbish to the truck?
B: Yes. You know    is our duty. We should help protect the environment.
A: I agree. , we must do something around the neighbourhood.
B: Sure. It is our duty to keep the environment clean and tidy. If we make a contribution to protecting the environment,  
A: That’s right. We mush try our best to make our country more beautiful. So we should     to improve the environment.

A. taking care of the environment B. the world will become much more beautiful C. do something useful D. after hearing the music E. Wherever live