Bunuel
The members of the United States Marine Corp (USMC) are famed for their intense devotion to one another. The Marine motto "Semper Fidelis" (Latin, "Always Faithful") is taken to connote, among other things, the lifelong devotion a Marine has to his or her comrades in the corp. Psychologists who study cohesion among groups have concluded that the USMC creates this intense bond through its unique Recruit Training program.
Which of the following, if true, most helps to justify the psychologists' position?
(A) Throughout their time in the Corp, whether during war or peace, Marines frequently engage in activities that reinforce the value of cooperation and camaraderie.
(B) New recruits are far more likely to engage in aloof behavior during the early stages of the USMC Recruit Training than during later stages.
(C) All branches of the armed forces have levels of internal cohesion much higher than typical civilian groups of similar aged individuals
(D) During their time in the USMC Recruit Training, new recruits have minimal interactions with people outside of the corp.
(E) It is well documented that intense professional training programs, such as medical school, form strong bonds among participants.
Official Explanation
In the argument, the unambiguous effect we want to explain is the intense "Semper Fi" cohesion of the Marines. That's not in question at all. The argument's conclusion suggests that the cause of this effect is the USMC's unique Recruit Training program. To strengthen this argument, we need something that isolates this cause, as opposed to some other cause.
(B) is the credited answer. If new recruits start out acting more independently at the beginning of the training, but are more bonded and cohesive by the end of the training, this strongly suggests that the training itself causes the group cohesion that we would like to explain. This justifies the psychologists' position.
(A) & (C) & (E) all suggest other possible causes of group cohesion, so they all are weakening the psychologists' position.
(D) is weakly suggestive, but not conclusive. It could be that new recruits are isolated during the training, during which they get very lonely, and only after the training they start to bond. This fact does not necessarily isolate the Recruit Training program itself as the sole cause of the intense group cohesion of the Marines.