LSAT PrepTest 43 Section 3 Question 19 Explanation | Logical Reasoning

I didn't write the following blog post. It was already on the blog when I took over the URL. The following blog post may contain mistakes. -Steve

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Here's a Logical Reasoning question from the June 2004 test.

The following is a chain of phrases for this argument:

Now plant fewer strains --> less diversity --> diseases have more impact

Many things might weaken this argument, so we won't pre-phrase. We'll just jump into the choices.

A) This is out of scope. At first glance, it would seem to weaken the argument since the argument talks about diseases in the past being minor. But it says some diseases that affect a single strain of plant were minor. That there were bad diseases in the past doesn't address the argument's point and so it doesn't weaken it.

B) Correct. This says that because there are seed banks to quickly replace crops that were diseased (and that these seeds are of different strains that the disease, which targets just a few strains, wouldn't hurt), the food supply wouldn't be devastated as the argument says. Since these seeds wouldn't be effected by the disease and could be used as replacements quickly, there is a good reason to believe the food supply would be saved and that the argument may be incorrect.

C) This is the opposite of what we want since it actually strengthens the argument. If plants were more resilient in the past, that supports the argument's claim that once-benign disease would now be devastating.

D) Out of scope. This choice is talking about how many different kinds of crops humans eat while the argument is talking about different strains (or types) of a single crop, and how farmers plant fewer strains these days. So, this choice doesn't address the argument. Noticing the crops/strains distinction is important here...be sure to read carefully!

E) Out of scope. The argument is talking about diseases, not insects or weeds.

Take-home points:

1) Use a chain of phrases (underline on the real test).

2) Get rid of choices that are out of scope (if they don't address the argument, they can't weaken it) and choices that are the opposite of what we want (in this case, they strengthen the argument rather than weaken it). Careful reading is crucial if you want to spot these.