Complete Question Explanation
Strengthen. The correct answer choice is (B)
This stimulus discusses a number of people who got sick eating local anchovies. The city of San Martin advised against eating these anchovies, because they were apparently tainted with a harmful neurotoxin called domoic acid. But because of a drop in the local population of a particular type of plankton, the anchovies are apparently safe to eat once again.
We should note that there is a leap from a premise regarding the drop in the plankton population to a conclusion about the safety of the anchovies. Since the question asks us to strengthen the conclusion, we should look for the answer choice that best explains why the decrease in plankton has led to lower levels of domoic acid and more safely edible anchovies.
Answer choice (A): If several types of plankton cause domoic acid in anchovies, this would weaken the conclusion that the noted drop in one particular plankton type would render the anchovies safe to eat.
Answer choice (B): This is the correct answer choice. This answer choice provides sufficient additional information to the stimulus to explain why the anchovies are now safe to eat. When the population of the plankton is extraordinarily large, the anchovies eat so much of it that they become toxic with domoic acid. This answer choice links the rogue elements of the stimulus as prephrased above.
Answer choice (C): While this answer choice does provide a link between the referenced plankton and domoic acid in the lab, it doesn’t necessarily explain how a drop in this particular plankton population would affect the presence or absence of domoic acid in nature. Because it does not fully explain why the anchovies are again safe to eat, this answer choice should be eliminated.
Answer choice (D): If a drop in P. australisi plankton is generally coincident with a drop in anchovies, then fewer plankton might result in fewer anchovies, but not necessarily safer anchovies. Therefore, this choice is incorrect.
Answer choice (E): This answer choice states that there must be significant quantities of domoic acid in the seawater in order to support a large population of P. australis (Large population significant domoic acid level). But the drop in population does not necessarily mean that the level of domoic acid dropped (large population significant domoic acid level). This is a Mistaken Negation, so this answer choice should be eliminated.