PrepTest 121, Section 2, Question 13

Working the answers

• A

  This accurately states the opening problem. It leaves out the proposed neutrino contribution and what the new evidence could mean, so it stops before the central development.

• B

  That resembles my own initial objection, not the scientists' position here. They seek additional matter within the gravitational explanation; the writer doesn't say they are beginning to reject that explanation.

• C
  Correct

  This captures the evidence for neutrino mass, the roughly 20 percent contribution, and the possibility of further progress. The last clause initially gives me pause: we are not promised a complete solution. But “could someday” describes a possibility beyond the present finding. The ending's hope for a broader understanding of elementary particles supports that direction. C does not say neutrinos alone already explain all the missing mass.

• D

  This focuses on the experimental finding in the third paragraph. Even putting aside its stronger word proves, it leaves out why neutrino mass matters to the dark matter problem.

• E

  The evidence does support neutrinos as a possible portion of the missing mass. Failing to explain all of it does not mean failing to explain any of it.