Why Is an Individual's Performance on a Task Undertaken with Others

Why is an individual's performance on a task undertaken with others better on complex tasks than on simple tasks?

A) There is less evaluation apprehension associated with simple tasks.
B) It actually depends on how the task will be evaluated.
C) When people become members of a group,they experience positive affect.
D) When people realize that their performance cannot be monitored or evaluated,they relax.
E) When people become members of a group,they are motivated to impress others.