PrepTest 124, Section 4, Question 24

Working the answers

• A

  Parathion doesn't affect cyclamen mites. It kills their predators. The fact that a chemical is an insecticide doesn't make it a useful fallback against this pest.

• B

  I could wonder about effects on other beneficial insects, but the writer doesn't discuss such effects or recommend caution pending their assessment. That would add a new concern to the stated position.

• C
  Correct

  At first, “only if” can sound like a rule that we must always try predators before any insecticide. Read its scope: the answer concerns “certain pest populations,” not every pest. For cases like the one described, where natural predation controls the pest effectively and a pesticide can undermine it, the author would favor relying on that control unless it proves inadequate.

  This doesn't make parathion an appropriate fallback; it remains ineffective against cyclamen mites. The supported recommendation is the limited preference for effective natural control, not approval of a particular replacement chemical.

• D

  Killing both types of mite doesn't establish that an insecticide should be preferred to predators. The writer supplies no such general preference.

• E

  “Generally” broadens the opening's limited claim, and the explanation that predators don't harm the crops is not established. The account demonstrates effective control in this case, not that universal safety advantage.