A、 Theories of how the universe evolved.
B、 Similarities between the planets in the solar system.
C、 Reason for the high density of earth.
D、 Theories of the origin of the Moon.

【正确答案】 D

【答案解析】主旨题。根据第一句话和通篇内容可知，本演讲主要讨论的是月球起源。因此，正确答案为D。

A、 Earth and the Moon traveled at different speeds.
B、 The Moon formed billions of years before Earth.
C、 Earth did not have enough gravitational pull.
D、 Earth and the Moon were too far from each other.

【正确答案】 C

【答案解析】细节题。根据But study shows that the young earth would not have had enough gravitational force to stop a body the size of a moon from traveling through the solar system and pull it into orbit．可知，年轻的地球没有足够的引力去阻止月球穿过太阳系，把它拉进轨道。因此，正确答案为C。

A、 The Moon has no water.
B、 The Moon' s materials came from Earth' s core.
C、 The Moon' s core differs from its surface.
D、 The Moon contains little iron.

【正确答案】 D

【答案解析】细节题。根据the moon contains almost no iron和相关信息可知本题正确答案是D。