【单选题】What is the talk mainly about
A.Differences between the planets in the solar system.
B.Methods of determining the composition of Earth and the Moon.
C.Why Earth has an iron core.
D.The origin of the Moon.
【单选题】What is the talk mainly about
A.Differences between the planets in the solar system.
B.Methods of determining the composition of Earth and the Moon.
C.Why Earth has an iron core.
D.The origin of the Moon.
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