On reentry, the Space Shuttle's protective heat tiles became extremely hot. (a) Was the mechanical energy of

Question:

On reentry, the Space Shuttle's protective heat tiles became extremely hot.
(a) Was the mechanical energy of the Shuttle-Earth system when the Shuttle landed greater than, less than, or the same as when it was in orbit?
(b) Choose the best explanation from among the following:
I. Dropping out of orbit increases the mechanical energy of the Shuttle.
II. Gravity is a conservative force.
III. A portion of the mechanical energy has been converted to heat energy.