The chief reason that family and friends are frequent targets of aggression is that
a. as obstacles, they're unremovable.
b. frustration-producing obstacles are often unclear.
c. they cause the most frustration.
d. they're convenient.

The correct answer is letter D. they're convenient. The chief reason that family and friends are frequent targets of aggression is that (D) they're convenient. Aggression is he feeling of harmful in terms of social interaction with the intention or goal of damaging other individual. Family and friends have already made a big interaction between each other.