If Earth Had a Pair of Identical Moons on Opposite

Multiple Choice

If Earth had a pair of identical moons on opposite sides of the same circular orbit, the center of gravity of the double-moon-Earth system would be

A) inside the Earth, but off center.
B) at the center of the Earth.
C) outside the Earth, but within the orbital path of the moons.
D) outside the Earth, but beyond the orbital path of the moons.