by demetri.blaisdell Fri Sep 16, 2011 12:41 pm
Good question. I love to see students going the extra mile and asking questions even when they get the right answer.
The result we need to explain is why it's safe to lift the ban. To do that, we will need to connect the levels of P. australis plankton to the reduction of domoic acid levels in the anchovies. (B) gives us exactly what we need. The anchovies apparently only eat enough P. australis to get poisonous levels of domoic acid when the population is large. Now that the population small, the levels will no longer be toxic.
(A) actually makes it more difficult to explain the result. If there are other types of plankton that cause toxicity, why should we reduce the ban when we only know that P. australis levels are down?
(C) is well out of scope. This background information gets us no closer to explaining why the ban should be lifted.
(D) is also out of scope. Though it connects the populations of the plankton and the anchovies, it tells us nothing about how toxic the fish are.
(E) is the most tempting wrong answer choice. There are two problems here. The most obvious is that it doesn't give us a mechanism by which the anchovies actually take in the domoic acid. In (B) we are told the anchovies eat the P. australis, but here we don't know that. We don't have any evidence that simply by swimming around in water with domoic acid, the fish will absorb or swallow in toxic levels.
The other slightly geekier problem with (E) is a negation issue. We are told: Big P. australis population --> high domoic acid. We can't use that piece of evidence to conclude that if there is a low population there are low levels of domoic acid. There could be another reason why the levels are low (predatory plankton, whales, mercury poisoning, etc).
I hope this helps clear up your confusion. (E) is a great wrong answer choice that brings up some really classic LSAT tricks. Let me know if you have any further questions.
Demetri