单选题 30. Scientists typically do their most creative work before the age of forty. It is commonly thought that this happens because aging by itself brings about a loss of creative capacity. However, studies show that a disproportionately large number of the scientists who produce highly creative work beyond the age of forty entered their field at an older age than is usual. Since by the age of forty the large majority of scientists have been working in their field for at least fifteen years, the studies' finding strongly suggests that the real reason why scientists over forty rarely produce highly creative work is not that they have simply aged but rather that they generally have spent too long in a given field.
In the argument given, the two portions in boldface play which of the following roles? ______

A、 The first is the position that the argument as a whole opposes; the second is an objection that has been raised against a position defended in the argument.
B、 The first is a claim that has been advanced in support of a position that the argument opposes; the second is a finding that has been used in support of that position.
C、 The first is an explanation that the argument challenges; the second is a finding that has been used in support of that explanation.
D、 The first is an explanation that the argument challenges; the second is a finding on which that challenge is based.
E、 The first is an explanation that the argument defends; the second is a finding that has been used to challenge that explanation.

【正确答案】 D

【答案解析】 D：第一部分是原因，而这一原因在However之后被文章反驳。第二部分是一项可用于反驳第一部分解释的发现，正确。
A：第一部分是原因，而非观点；第二部分反驳的是文章之前给的一个解释，而非质疑结论(explanation也可以指代原因)。
B：第二部分用于反驳第一部分给出的解释，而非支持第一部分的观点。
C：第一部分是原因，而这一原因在However之后被文章反驳。第二部分反驳了该解释。
E：第一部分是文章反对的解释，分号后正确。