Explanation
The point of the ice core method for temperatures that the
isotope ratios in the ice indicate what the temperature was at a point the
past. That's a pretty basic fact about the technique, but we can compare to the
answer choices and see how far it gets us. Answer choice (A) might sound at
first like it describes some sort of inconsistency, but, in fact, answer choice
(A) would imply that the technique is working, or at least might be working
correctly. So (A) is out. (B) is similar to (A), but it mentions getting
different results for different extraction
methods. That contradicts one of the big advantages of this technique, as
stated in paragraph three--near the end of the paragraph, it talks about using
big drills and hand drills, for example. If we have eliminated an advantage of
the technique, we have made the technique less useful. Answer choices (C) and
(E) are plausible but are not supported by the passage. Choice (D) is out on similar
grounds to (A).
The correct answer is (B).
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