This best captures the author’s point, which is that groupthink is a phenomenon that can negatively affect decision-making when they’re high cohesiveness. She expresses this point in P2 and supports it with a description of the causal mechanism underlying groupthink.

Not supported, because the author never suggests that a group member’s awareness of cohesion and the role it plays in decisionmaking has any effect on the likelihood of groupthink occurring. Since (B) is not supported, it can’t be the main point.

Although the author notes that certain researchers believe groupthink was at play in certain diplomatic and military disasters, the point of the passage isn’t to emphasize groupthink’s occurrence in diplomacy and military affairs. Groupthink might occur in any group in which there is high cohesiveness. Diplomacy and military affairs are simply two examples where it might occur, but we have no reason to think it isn’t just as likely to occur in other contexts.

The author never suggests that low cohesion can be desirable due to the risk of cohesion. P1 describes the negative effects of low cohesion, and the author never suggests those effects are preferable to the effects of groupthink.

The author notes at the end that research is important for identifying other factors that determine whether high cohesion will produce groupthink. However, a comment about future research is too narrow to be the main point. The author’s discussion of groupthink is much broader. It encompasses the idea that high cohesion creates the conditions for groupthink, which (E) doesn’t express.