(a) Is the amount of energy required to get a spacecraft from the Earth to the Moon greater than, less than, or equal to the energy required to get the same spacecraft from the Moon to the Earth?

(b) Choose the best explanation from among the following:

I. The escape speed of the Moon is less than that of the Earth; therefore, less energy is required to leave the Moon.

II. The situation is symmetric, and hence the same amount of energy is required to travel in either direction.

III. It takes more energy to go from the Moon to the Earth because the Moon is orbiting the Earth.