“________run in the hallways, Mike.”  "Sorry, Ms Clark.”
A. Don't             B.  Please        C. Let's

________ run in the hallways.

1. A.
   Not
2. B.
   Don't
3. C.
   Mustn't
4. D.
   Can't

________ run in the hallways．It’s dangerous．

1. A.
   Don’t
2. B.
   Can’t
3. C.
   Mustn’t
4. D.
   Aren’t