用恰当的词语填空，完成对话。每空一词。

A: Hi! Linda!

B: Hi! Michael!

A: What bad 1_______! There is so much sand and dirt in the air.

B: So it is. Have you 2_______ of the sandstorm?

A: No, I haven't. What's that?

B: There is lots of sand flying in the air when the wind is 3_______ strongly.

    So we can't see anything clearly outside.

A: But what 4_______ these sandstorms?

B: People do something harmful to destroy the environment, such as cutting down too many trees.

A: That's too bad. I think we still need to work hard to 5_______ our environment.

B: Yes, I agree with you.