Understanding the argument -
Scientists typically do their most creative work before the age of forty. - Fact
It is commonly thought that this happens because aging by itself brings about a loss of creative capacity. - Fact. Reason for the first fact. The argument later challenges this explanation.
However, studies show that
of scientists who produce highly creative work beyond the age of forty, a disproportionately large number entered their field at an older age than is usual. - Fact + Claim to challenge the above reasoning.
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 aged but rather that
scientists over forty have generally spent too long in their field. - Supporting premise + conclusion - not earlier reason but the alternate reasoning (2nd BF is alternate reasoning.
Option Elimination -
(A) The first is a claim (ok), the accuracy of which is at issue in the argument (No, the accuracy of the first claim is not at issue); the second is a conclusion drawn on the basis of that claim (ok) - overall no.
(B) The first is an objection that has been raised against a position defended in the argument (No, both the BF go in the same direction); the second is that position. (ok) - Overall, no.
(C) The first is evidence that has been used to support an explanation that the argument challenges (No. The argument challenges the earlier reasoning, and the first BF challenges that and does not support it); the second is that explanation. (No. the 2nd is not an explanation that the argument challenges) - No.
(D) The first is evidence that has been used to support an explanation that the argument challenges; (No. The argument challenges the earlier reasoning, and the first BF challenges that and does not support it) the second is a competing explanation that the argument favors. (ok) - overall no.
(E) The first provides evidence to support an explanation that the argument favors; (ok) the second is that explanation. (ok)