PrepTest 145, Section 4, Question 26

What we’re looking for

Working the answers

• A

  This promises too much. The plan doesn't require that no creature capable of causing ecological damage in any new habitat ever enters a tank. A creature collected in one part of the open ocean might cause problems in another open-ocean habitat while being unable to survive at the coast where this ship will release it. That possibility wouldn't defeat the proposed coastal-water exchange. A's broad guarantee goes beyond what the plan needs.

• B

  The argument doesn't require calm air and flat seas to be the only conditions in which the exchange is possible. Perhaps ships can safely do it in a wider range of conditions. That would leave the proposal intact. A restriction to ideal weather might affect when the plan can be used, but that specific restriction is not an assumption the author must make.

• C

  This resembles my concern about a creature doing damage without surviving for long. But C makes a much broader claim: ecological havoc has rarely, if ever, occurred unless the creatures could survive in the new habitat after being deposited there by ships. A viable way to address the ballast problem doesn't require that sweeping rule about what ecological harm depends on. Even if some creatures cause damage before dying, the exchange could still reduce the frequency or extent of damage enough to be worthwhile. My initial concern deserves investigation, but any remaining harm wouldn't automatically make the proposal unworkable. C demands more than the argument needs.

• D

  The passage says ships adjust ballast when loading and unloading cargo. It doesn't say those are the only occasions when they do so. There might be other reasons to change the water level, and the proposed exchange could still be viable. The argument doesn't depend on this exclusive description of current practice.

• E
  Correct

  Can ships actually perform the exchange while remaining adequately stable? That is a different concern from the ecological ones I predicted. The tanks provide stability, so emptying them in the middle of the ocean cannot be treated as automatically safe.

  If no oceangoing ship could maintain adequate stability during the process, this would fail as a viable proposal, regardless of what happens to the transported creatures. The author therefore needs at least some ships to be able to do it safely. E makes that limited requirement; it doesn't demand that every ship can perform the exchange under every condition.