The key      the earth is to change the way      we live.

1. A.
   to save; /
2. B.
   to saving; /
3. C.
   to save; how
4. D.
   to saving; how

The key       the earth is to change the way       we live.

A. to save; /                              B. to saving; /

C. to save; how                    D. to saving; how

 The key      the earth is to change the way      we live.

The key      the earth is to change the way      we live.