Hi,
I chose E and below is my reasoning:
Main Conclusion: "Such reasoning might well be overoptimistic"
(note that MC is the author's or the passage's conclusion unless otherwise stated)
1st sentence: present a fact that "several bank's top executives have been buying shares ..., relieve the bank's depositors. 1st BF is a Cause, for some effects that the author thinks it's a reversed cause and effect.
2nd sentence: further breakdown of the cause and effect in 1st sentence.
3rd sentence: Main conclusion, and explanation for the main conclusion that the above cause and effect is actually a reversed cause and effect. Meaning the effect is actually the cause (top exec bought shares to defer the rumors)
Answer choice:
(a) The first describes evidence that has been taken as supporting a conclusion; the second gives a reason for questioning that support.
=> the "conclusion" in A is the conclusion of the depositors, not of the passage nor of the authors.
(e) The first 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.
=> follow the right logic of the passage. The first sentence provides a fact, a going on event that the author later seeks to explain, and the second provides evidence as reasoning as a base for the main conclusion "Such reasoning might well be overoptimistic"
Also, if answer (A) is correct, then I am extremely confused for the so called "conclusion" in GMAT passages as it did not explicitly stated "the depositor's conclusion" in answer A for it to stand correct.