Understanding the argument -
Flagpole Army Base in Oregon and Klondike Army Base in Alaska are similar bases with similar duty loads. - Fact
Despite the similarities, Klondike always has had more men than Flagpole has. - Fact
Clearly, each soldier at Klondike must have to perform a smaller share of the duties, and therefore soldiers at Klondike must have more free time than do soldiers at Flagpole. - Intermediate conclusion + The main conclusion.
Option Elimination - The scope of the argument is to check the validity of the conclusion, which is "soldiers at Klondike must have more free time than do soldiers at Flagpole."
(A) Whether those recruits who are in a position to choose, choose Flagpole over Klondike. - Choice of recruits is out of scope.
(B) Whether the officers administering the Flagpole and Klondike bases have had similar training. - Officer's training is out of scope.
(C) Whether the morale level at Klondike is higher than the morale at Flagpole. - out of scope.
(D) Whether regular furloughs from Klondike are longer than furloughs from Flagpole, to account for added travel time. - If many soldiers are on furloughs, then the soldiers will not have less but more work to do. The validity of the conclusion is in question. But if it is otherwise, then ok. So this is ok.
(E) Whether similar numbers of soldiers are stationed at comparable bases throughout the country. - "Throughout the country" is out of scope. We are just talking about Oregon and Alaska here.