official Explanation for Q3
This is an "EXCEPT" question. We expect that the passage clearly implies four of the answers, and for the last, it either implies something else or simply is not clear on that point. This last one, the one not clearly implied, is the right answer.
In the last sentence, the passage clearly says we know more about the logical reasoning in Chinese math because of this one work that shows proofs. If we know less about the logical reasoning in ancient Mesopotamian math, it's because those works don't show proofs. Choice (A) is clearly implied, so it is not the answer to the EXCEPT question.
The passage clearly says "This fact, which was long unrecognized, …" --- in other word, the first folks studying this did not realize that the commentaries and sub-commentaries on the Jiuzhang Suanshu provided proofs. Choice (B) is clearly implied, so it is not the answer to the EXCEPT question.
The passage clearly says that proofs "justify" mathematical results, and explain why it is true. In other words, proofs "demonstrate the logical argument underlying a mathematical result". Choice (C) is clearly implied, so it is not the answer to the EXCEPT question.
The passage clearly says that the Jiuzhang Suanshu "served as a reference for [Chinese mathematics] over a long period of its history." Therefore, it is quite reasonable to infer that most Chinese mathematicians between 1000 and 1500 would have known about it. Choice (D) is clearly implied, so it is not the answer to the EXCEPT question.
The passage talks about "justification" in terms of the logical justification a mathematical proof implies. Nowhere does it discuss people justifying themselves. Choice (E) is not implied, so this is the correct answer to the EXCEPT question.
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