Which Is the Primary Method for Studying the Classification of Autonomic

Which is the primary method for studying the classification of autonomic drugs?

A) Defining which receptor sites are stimulated.
B) Contrasting nicotinic agonists with muscarinic agonists.
C) Comparing two groups of drugs: the adrenergics and cholinergics.
D) The stimulation and inhibition of the sympathetic nervous system and parasympathetic nervous system.