Final answer:
Nitric oxide is not a neurotransmitter used by the sympathetic nervous system; it is involved in vasodilation. Norepinephrine and acetylcholine are the neurotransmitters released by the sympathetic nervous system. The correct option is A.
Step-by-step explanation:
In the context of the sympathetic nervous system, norepinephrine and acetylcholine function as neurotransmitters. Norepinephrine is the primary neurotransmitter released by postganglionic neurons in the sympathetic nervous system and has various effects such as increasing heart rate and dilating the pupils.
Acetylcholine is involved as well, but it is released by preganglionic neurons in both the sympathetic and parasympathetic nervous systems.
However, nitric oxide is a gasotransmitter that mainly functions as a signaling molecule and is involved in the process of vasodilation, it is not traditionally considered a neurotransmitter in the sympathetic nervous system. Therefore, option a) nitric oxide is the correct answer.