#21- Must be True, Main Point

[lsat2016]

Could anyone explain the difference between A & E?

Thanks!!

[Clay Cooper]

Hi Lsat2016,

Thanks for your question.

Answer choice E is too broad. It mentions 'mechanisms' and 'gases that could bind competitively'; we are only told about one mechanism - C4 photosynthesis - and only one such gas that could bind competitively - oxygen.

[chian9010]

Is B because the "higher qualities of nutrients"? If we delete the higher quality part, will it be the correct answer?

[Brook Miscoski]

Chian,

The passage is about crop yield, not nutrients. B is about the wrong topic (nutrients), and A is about the correct topic (productivity). So even deleting the reference to quality, B would still be wrong.

[powerscoreQasker]

Thanks for these points - I somehow missed that, per the passage, C-4 photosynthesis also occurs in the leaf, just like normal photosynthesis. On the basis of that error I used the mention of the leaves in E) to eliminate E). Would it be correct to say that another problem with E) is that E) claims that the gases can't enter the leaves at all, whereas the passage says the gases can't enter a specific structure inside the leaves (though it says nothing about whether gases can enter other parts of the leaves)?

[Jeremy Press]

Hi Qasker,

You're working harder than you need to on this Main Point question. Sometimes Main Point answers in Reading Comprehension are wrong because they incorrectly represent the facts of the passage. But this shouldn't be the only (or even the most important) thing you're looking at to eliminate an answer on such questions. Often an answer choice is wrong on a Main Point question simply because it doesn't address the most important ideas that the author is trying to convey to the reader. What is the basic question that this passage starts by asking? It's at the end of the first paragraph: "why are maize and a few similar crops so much more bountiful than others?" This is the author's main concern. The author wants to answer for the reader why maize is such a productive crop. The passage goes on to supply a simple answer to this question (although cloaked in lots of complicated science), which it states at the very end: "C-4 photosynthesis... plants [such as] sugar cane, rice, and maize are among the world’s most productive crops." The author is making a simple causal argument: C4 photosynthesis causes the greater productivity of certain crops.

The problem with answer choice E is that it does not clearly state this causal argument/relationship which is the main point of the passage. Answer choice E talks about the mechanisms C4 photosynthesis uses. But it never states that these mechanisms cause the productivity of the crops. That's enough to eliminate it!

I hope this helps!

[powerscoreQasker]

Jeremy,

Thanks for the answer. And I appreciate you keeping the focus on the bigger problem with E) - that it doesn't summarize the main idea of the passage. The observation about whether oxygen enters the leaves of the C-4 photosynthesizing plants or not occurred to me as another reason why E) doesn't fit. From the RC sections I've done, a lot of main point question answer choices will have multiple problems, such as failing to capture the main point while misstating a detail or two. That's what I think E) is, too - without the error about oxygen it would still be correct to eliminate E), but that error gives the test taker one extra opportunity to correctly eliminate the answer choice.