Explanation
Correct answer: B.
Choice B is the best answer. A consistent age difference of 2 billion years between certain stars within the thick disk would support the claim that the thick disk formed in two phases instead of one, with the second phase beginning 2 billion years after the first phase.
Why the other choices are wrong
Choice A
Choice A is incorrect. This choice doesn’t support the claim. The researchers base their claim on their study of stars inside the thick disk of the Milky Way. This choice makes a comparison to stars in other galaxies, which isn’t relevant.
Choice C
Choice C is incorrect. This choice doesn’t support the claim. The researchers base their claim on their study of stars inside the thick disk. This choice makes a comparison to the thin disk, which isn’t relevant.
Choice D
Choice D is incorrect. This choice doesn’t support the claim. It’s too general. The claim is specifically about the thick disk.