Final answer:
M3 receptors are G protein-coupled receptors on the target tissues of postganglionic parasympathetic fibers, and are present on airway smooth muscle and submucosal glands.
Step-by-step explanation:
The question pertains to the localization of M3 receptors, which are a subtype of muscarinic receptors involved in the function of the parasympathetic nervous system. According to the provided information, all preganglionic fibers, whether sympathetic or parasympathetic, release acetylcholine (ACh) and stimulate nicotinic receptors. However, the postganglionic parasympathetic fibers also release ACh, but their targets have muscarinic receptors. Specifically, M3 receptors are G protein-coupled receptors found on the target tissues of postganglionic parasympathetic fibers. These include the airway smooth muscle and submucosal glands, among other locations. Therefore, the correct answer to the question 'M3 receptors are present on which of the following?' is c. Airway smooth muscle, submucosal glands, as these tissues are well-known targets of the postganglionic parasympathetic nervous system that express M3 receptors.