Final answer:
The parasympathetic nervous system, which releases serotonin, is responsible for relaxation and decreased metabolic activity. Therefore correct option is B
Step-by-step explanation:
The correct answer is B) Parasympathetic; serotonin.
The parasympathetic nervous system is responsible for relaxing the body and promoting rest and digestion. It releases serotonin, a neurotransmitter that decreases metabolic activity.
For example, when you are relaxing after a meal, your parasympathetic nervous system is active, which slows down your heart rate, lowers your blood pressure, and stimulates digestion.