Explanation

The passage outlines a conflict between two standard theories — one of planet formation, the other of companion stars — and observations of one large body, and later two others, orbiting close to a star. The question asks what would resolve this conflict without casting doubt on either one of the theories.

Choice B is correct: if, as it asserts, it is possible for a planet to be formed relatively far from a star and later move closer to it, then the observed large bodies found close to Upsilon Andromedae can be planets without casting doubt on the standard theory of planet formation. This explanation also leaves the standard theory of companion stars intact.

Choice A is incorrect because it describes difficulties with discovering a small planet far from a star, not anything pertaining to a large body near a star. Choice C is incorrect as well, since whatever the relative size and position of the three bodies may be, all three appear to be too close according to the standard theories.

Choice D is incorrect because the pervasiveness of stars with multiple orbiting bodies has nothing to do with the status of the large bodies discussed in the passage.

Choice E is similarly irrelevant and thus incorrect: information about the brightness of a star relative to its companion star does not help clarify the status of the large bodies discussed in the passage.
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How it is B

Would you please explain ,how to solve this kind of question?which one is premise of statement and which one is conclusion?

This is a discrepancy question, and as whole it pertains to the family of inference questions.

• No Conclusions! These are made up entirely of premises
• No Assumptions either!
• Two main question types: Inference and Explain a Discrepancy

You need to solve the paradox inside. How could we explain the near planets but according the standar theory we cannot have more than one planet companion ?'

The gravity, so the attraction of an external bosy near the main one we take into account, can solve the discrepancy.

Hope this hleps.

Regards
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