Final answer:
Laughter boosts immune function and is associated with positive health effects. The correct therapeutic effect of laughter according to the provided options is that it activates the immune system.
Step-by-step explanation:
The nurse is teaching a novice nurse about the therapeutic effects of laughter, and one correct therapeutic effect is that it activates the immune system. When discussing the body's response to stress and emotion, we often refer to the involvement of the sympathetic nervous system and the secretion of hormones like epinephrine and norepinephrine, which can lead to increased heart rate and breathing rate, among other things. However, laughter is generally associated with positive effects, like boosting immune function, rather than causing shallow breathing or decreasing heart rate. Thus, the correct answer to the student's question is 'a) It activates the immune system.'