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  3. At a certain period in Earth’s history, its atmosphere contained almost no oxygen, although plants were producing vast quantitie

At a certain period in Earth’s history, its atmosphere contained almost no oxygen, although plants were producing vast quantitie

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问题 At a certain period in Earth’s history, its atmosphere contained almost no oxygen, although plants were producing vast quantities of oxygen. As a way of reconciling these two facts, scientists have hypothesized that nearly all of the oxygen being produced was taken up by iron on Earth s surface. Clearly, however, this explanation is inadequate. New studies show that the amount of iron on Earth’s surface was not sufficient to absorb anywhere near as much oxygen as was being produced. Therefore, something in addition to the iron on Earth’s surface must have absorbed much of the oxygen produced by plant life.
In the argument given, the two portions in boldface play which of the following roles?
选项 A、The first is a claim made by the argument in support of a certain position; the second is that position.
B、The first is a judgment made by the argument about a certain explanation; the second is that explanation.
C、The first expresses the argument’s dismissal of an objection to the position it seeks to establish; the second is that position.
D、The first sums up the argument’s position with regard to a certain hypothesis; the second provides grounds for that position.
E、The first is a concession by the argument that its initial formulation of the position it seeks to establish requires modification; the second presents that position in a modified form.
答案D
解析 The passage presents an argument and the question asks you to identify the role the portions highlighted in boldface play in that argument. The first step in responding is to read through the passage quickly to get an understanding of what is being said. Then it is possible to go back and assess how the parts of the passage fit together into an argument.
In this passage the first sentence presents two pieces of information that seem to be in conflict—the atmosphere contained almost no oxygen even though plants were producing so much of it. The second sentence presents a hypothetical explanation that has been proposed for reconciling the discrepancy—that oxygen was absorbed by iron. The next sentence calls this hypothetical explanation inadequate and the following sentence gives a reason for that judgment—that there was insufficient iron for the proposed explanation to work. Finally, the last sentence draws the conclusion that there must have been something in addition to iron to absorb the oxygen.
Since the highlighted portions in the passage represent the main content of the third and fourth sentences, the task in this question is to find the answer choice whose two parts fit those sentences’ roles. It can be seen that answer Choice D fits the requirement: the third sentence does sum up the argument’s position about a hypothesis, and the fourth sentence gives grounds for the third. Therefore Choice D is the correct answer.
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