On a certain deep space mission, the vessel’s computer indicated that there was insufficient oxygen in the ship’s atmosphere to keep all six crew members alive until they reached the closest space station. The ship’s doctor reasoned that the amount of oxygen needed by the crew had been underestimated. However, this reasoning was incorrect. The ship’s biologist checked the oxygen records and, in fact, more than enough oxygen had been budgeted for the mission. Additionally, the ship’s engineer confirmed that the ship was not leaking air. Therefore, something other than the crew members must have been responsible for the oxygen shortage.

In the argument given, the two portions in boldface play which of the following roles?

A. The first is an assertion made by the argument in support of a certain position; the second is that position.
B. The first is an opinion made by the argument about a certain explanation; the second is that explanation.
C. The first is the argument’s dismissal of an objection to the position it tries to establish; the second is that position.
D. The first summarizes the argument’s position with regard to a certain hypothesis; the second provides support for that position.
E. The first is an admission by the argument that its position is flawed; the second corrects the flaw in the argument’s position.