When humans started launching rockets into outer space, they needed to make certain the rockets had enough power to escape Earth's gravitational field. Which of these would have made it much more difficult for humans to design rockets capable of reaching outer space?

A.

if the Earth was much less massive than it is

B.

if the Moon spun on its axis more quickly

C.

if the Earth was much more massive than it is

D.

if the Moon was much more massive than it is