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This Reading Comprehension question is from the October 2004 LSAT.
The questions asks us to see what would bolster the author's contention in the passage's final sentence, which is that the current state of that land can't be understood without looking at the actions of the Chinese settlers. There could be many things that would support that claim, so we won't try to pre-phrase here. Instead, let's start going through the answer choices and eliminating them:
A) Outside the question's scope. The last sentence, which is our focus, talks about how irrigation and major production of specialty crops happened, not about how specialty crops as a group became more popular.
B) Correct. This mentions how the land got irrigated and became very productive, and says that the Chinese settlers were an integral part of this, which supports the author's claim that how the irrigation and productivity happened can't be understood without looking at the contributions of the Chinese settlers.
C) Beyond the question's scope. It doesn't help because it doesn't mention the Chinese specifically (and it's supposed to support the claim that the Chinese had a big impact) and also doesn't explain how the land got irrigated and became productive but merely that it could do so. Not what we want.
D) Outside the question's scope. Like choice C, it never mentions the Chinese, and thus doesn't support the author's claim. It also doesn't really say how this land, that owned by the Chinese, got irrigated and became productive. It just says that irrigation methods have improved. Again, not what we need to support the author's claim.
E) Wrong for the same reasons as C and D; beyond the question's scope. Doesn't mention the Chinese or how their contribution to irrigation/productivity in this region was indispensable, and thus does not answer the question by supporting the author's claim.
Remember:
1) On a question in which there are a lot of possible answers, it may not save time to pre-phrase. You may do better to just start eliminating answer choices.
2) Watch out for answer choices beyond the scope of the question (or, for that matter, the passage). If the answer choice is talking about something that has nothing to do with the question, it's not going to be right. Seems obvious, but it's a powerful strategy if you can apply it well.
