被一道黑脸题目折磨，求大侠相助！！！！！！！！！！

rebeccadu1

Since it has become known that several of a bank’s top executives have been buying shares in their own bank, the bank’s depositors, who had been worried by rumors that the bank faced impending financial collapse, have been greatly relieved.  They reason that since top executives evidently have faith in the bank’s financial soundness, those worrisome rumors must be false.  They might well be overoptimistic, however since corporate executives have sometimes bought shares in their own company in a calculated attempt to dispel negative rumors about the company’s health.
In the argument given, the two boldfaced portions play which of the following roles?

(A) The first describes evidence that has been taken as supporting a conclusion; the second gives a reason for questioning that support.
(B) The first describes evidence that has been taken as supporting a conclusion; the second states a contrary conclusion that is the main conclusion of the argument.
(C) The first provides evidence in support of the main conclusion of the argument; the second states that conclusion.
(D) The fi rst describes the circumstance that the argument as a whole seeks to explain; the second gives the
explanation that the argument seeks to establish.
(E) The fi rst describes the circumstance that the argument as a whole seeks to explain; the second provides evidence in support of the explanation that the argument seeks to establish

想问一下题目中的D 为什么不对啊。。。

skyemotion

They might well be overoptimistic, however
表示However前后的方向相反。
所以D不对。