Video Explanation

Text Explanation

For this question, much like other questions involving arguments, it’s critical that you identify the three parts of the argument: the premise(s), the conclusion, and the assumption. Since this question directly asks you to find which answer choice weakens the argument, it’s critical to find the assumption, since by weakening the assumption, you weaken the argument, and find the answer to this problem.

We read that the Malbec grape has become the main varietal, or type of grape, grown in Argentina. We also know that the Malbec is usually grown at low altitude, but in Argentina, it’s grown at high altitude. Those are the two premises: the Malbec is the main grape type grown in Argentina, and that while it’s typically grown at low altitudes, it’s grown at high altitude in Argentina.

After that, we see the conclusion: that Argentine winegrowers should grow the Malbec at high elevations. But why? That’s where the assumption -- the unstated part of the argument that bridges the premises and conclusion -- comes in.

We know from the premise that the Malbec is not typically grown at high altitudes, like it is in Argentina, and that the Malbec originated from France, and is typically grown in low-lying regions. So to bridge these premises to the assumption, we can say the assumption is that Malbec growers in Argentina should move Malbec grapes from high to low altitudes to have more success.

Now let’s see which of the answers most weakens this assumption.

(A): This answer is discussing the Bordeaux grape, which is irrelevant to the argument on the Malbec. (A) is out of scope and doesn’t work.

(B): First, we already know that the Malbec grows at high altitudes because it’s the main varietal in Argentina. Second, this choice refers to “some varietals”, which might not necessarily apply to the Malbec. (B) is wrong for those two reasons.

(C): This answer choice is very tempting. It gives a very good reason as to why farmers might not want to move the Malbec to low altitudes, since the soil at high altitudes has nutrients that can help the Malbec flourish.

However, this answer has two flaws. The first flaw is similar to one found in choice (B): it refers to “most” varietals, and the nutrients that help most varietals might not help the Malbec. Second, just because the soil at high altitudes has nutrients doesn’t disqualify the soil at low altitudes from having those nutrients as well. If all of the other answer choices are extremely flawed, this could be a correct answer; after all, we’re looking for the answer which most weakens the argument, not a 100% perfect answer. With that said, we’ll press on and see if either (D) or (E) is better.

(D): Here we go! We know that the Malbec is susceptible, or vulnerable or weak to, a plant louse that resides at low altitudes. If the Malbec varietal specifically is weak to a plant louse, a parasitic insect, at low altitudes, that would be a very good reason to keep the Malbec at high altitude. 

Since this answer refers to a threat specific to the Malbec grape at low altitudes, it weakens the argument that the Malbec should grow in low-lying areas -- if it did, it would be vulnerable to a plant louse and would not grow as well. (D) is very likely to be correct, but we need to check E to make sure.

(E): The argument doesn’t mention popularity or other countries at all: it’s only concerned with whether the Malbec should be grown at high or low altitudes. (E) misses the mark.

(D) is the answer that most weakens the argument, so it is the correct answer.

Takeaway:

If you’re having trouble evaluating the answers in a question that asks about an argument, focus on specifics: does the answer directly mention something mentioned in the passage, or does it use a general word like “some”? That dimension is tested a lot in these types of questions, so be sure to keep that in mind.