A nurse is taking care of an adult client who throws a temper tantrum because he does not get his own way. Which defense mechanism is the adult client displaying?

The correct answer is D: Regression. Regression is a defense mechanism where an individual reverts to a behavior from an earlier stage of development in response to stressful situations. In this case, the adult client throwing a temper tantrum is exhibiting behavior reminiscent of a child's response to not getting their way. This behavior is a form of regression as the client is reverting to a less mature way of coping with their emotions. Repression (A) involves unconsciously blocking out thoughts or memories. Rationalization (B) is creating logical explanations to justify unacceptable behavior. Reaction formation (C) is expressing the opposite of one's true feelings. In this scenario, the adult client's behavior aligns most closely with regression as they are displaying childish behavior in response to not getting their way.