根据对话内容,用方框中所给单词的恰当形式填空。
forget , crowded , prevent , needn’t , build
A:Welcome to our school , Dr . King.
B:Thank you.
A:Could you give us some suggestions to the flu?
B:Sure. First , doing sports much can us up.
A:Must we clean our rooms every day?
B:No, you . But it’s necessary to keep the air fresh.
A:What should we do then?
B:Don’t to wash hands before meals.
A:That’s fine.
B:And you had better keep away from places.
A:Thanks for your advice.