Groupthink is caused by:

A) team cohesiveness.
B) an opinionated team leader.
C) isolation of the team from outsiders.
D) stress due to an external threat.
E) All of these factors cause groupthink.

All of these factors can contribute to groupthink. Team cohesiveness can lead to a desire for unanimous agreement, an opinionated team leader can discourage dissenting opinions, isolation from outsiders can limit exposure to alternative viewpoints, and stress can increase the desire for quick and easy solutions. It is important to be aware of these factors and actively work to combat groupthink in order to make better decisions.