Answer:
Impact Theory
Step-by-step explanation:
"The Impact Theory has two advantages over other theories about the moon's origin. First, other theories cannot explain the differences in the composition of the earth and moon. . . If Earth and a Mars-sized object collided, their iron-rich cores most likely would have merged into the earth's core. The collision would eject dust primarily from the mantles of the two bodies. This would explain why the moon's composition is similar to the composition of Earth's mantle."
The co-formation theory is not supported by that discovery because its composition should have been the same. "Although the moon is similar in age to Earth, its composition is very different. Earth is 31% iron, with most of the iron contained in the earth's core. The moon is only 8-12% iron. This difference is hard to explain if the earth and moon formed from the same material."
Therefore, it is not the co-formation theory, it is the impact theory.