This doesn’t strengthen, because we have no evidence that the groups subject to group think were highly cohesive, or that the groups that didn’t have groupthink were not highly cohesive.

Dissent can be a result of a highly cohesive group. It doesn’t tell us whether groupthink is more likely to occur in a highly cohesive group, however, because groupthink doesn’t involve dissent.

This strengthens by providing evidence that without the condition of high cohesion, groupthink doesn’t occur. When group members generally distrust each other, that signifies lack of high cohesion.

This suggests that groupthink might occur under conditions of low cohesion (since factions that oppose each other are evidence of low cohesion). This doesn’t support the author’s claim that high cohesion can produce groupthink.

This doesn’t support the author’s connection between high cohesion and groupthink, since voluntary deference isn’t indicative of high cohesion over low cohesion. Remember, in a low cohesion group, group members might be deterred from voicing their true opinions. This is a kind of voluntary deference to group opinion that isn’t associated with high cohesion.