Everyone here will thank the firefighters for the things they have done to prevent fires _______ the environment safer.?

A. make　B. to making ?

C. to make D. from making?

Everyone here will thank the firefighters for the things they have done to prevent fires _______ the environment safer.

1. A.
   make
2. B.
   to making
3. C.
   to make
4. D.
   from making

Everyone here will thank the firefighters for the things they have done to prevent fires _________ the environment safer.

  A. make             B. to making          C. to make             D. from making

Everyone here will thank the firefighters for the things they have done to prevent fires ________ the environment safer.

[　　]

Everyone here will thank the firefighters for the things they have done to prevent fires ________ the environment safer.

[　　]