Critical Reasoning

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 fi nancial collapse,have been greatly relieved. They reason that, since top executives evidently have faith in the bank's fi nancial soundness, those worrisome rumors must be false. Such reasoning might well be overoptimistic, however, since corporate executives have been known to buy 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 fi rst describes evidence that has been taken as supporting a conclusion; the second gives a reason for questioning that support.
(B) The fi rst 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 fi rst 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.

can't understand why 1st BF doesn't "describes the circumstance that the argument as a whole seeks to explain" - we are given a circumstance than exec. are buying shares. 1st one conclusion is deduced and then arg. gives evidence to show that there can be other reason.