PrepTest 159, Section 2, Question 15
Since 1929, cosmologists have known that the universe(446 more words not shown)
Which one of the following(9 more words not shown)
- AResearchers hypothesize the(13 more words not shown)
- BThough there is(20 more words not shown)
- CThe current proposals(20 more words not shown)
- DScientists have proposed(16 more words not shown)
- EThe best explanation(16 more words not shown)
Reading the passage
We already predicted the central idea: scientists have two explanations for the accelerating expansion, and each raises a difficulty for the current scientific picture. Dark energy faces a mismatch in the proposed energy source; the alternative requires changing how gravity is understood.
What we’re looking for
The possible testing advantage at the end belongs within that comparison. It doesn't turn the discussion into an endorsement of the second theory.
Working the answers
- A
This describes the first explanation but leaves out the gravity-based alternative. The account isn't only about why dark energy was proposed.
- B
The author describes evidence supporting dark energy, including studies of the big bang's afterglow. The specific problem is the discrepancy in the proposed vacuum energy, not a general conclusion that dark energy has little evidence. B also omits the alternative explanation.
- C
The proposed change to gravity belongs to the second theory, which does not invoke dark energy. C incorrectly attaches that change to proposals about dark energy and misses the two-theory structure.
- DCorrect
This includes both explanations and the challenge each poses. Neither is presented as fitting smoothly into the accepted picture: the first has an energy mismatch, while the second requires revising Einstein's account of gravity.
- E
The second theory may be easier to test, but the author doesn't establish that it is the best explanation. An advantage in testing a theory isn't proof that its account is right.
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