Which of the following increases the tendency for groupthink? a. group is socially engaging with nonmembers often b. group has not chosen a respected leader c. group is under pressure to make a decision d. group lacks cohesiveness

The one that increases the tendency for groupthink: C. group is under pressure to make a decision 

A groupthink happen when ALL members of the group have the tendency to conform with one another.
When the group is under pressure to make a decision, most people wouldn't want to held responsible by making a wrong decision. So most people will prefer to hear the first person that make an idea and follow it to let that person took the fall.