The gravity on the earth is much ______ that on the moon, do you know why?

The gravity on the earth is much ______ that on the moon, do you know why?

1. A.
   as strong as
2. B.
   strong than
3. C.
   so strong than
4. D.
   stronger than

The gravity on the earth is much ______ that on the moon, do you know why?

A. as strong as     B. strong than       C. so strong than          D. stronger than

The gravity on the earth is much ______ that on the moon, do you know why?