Why is Aplysia an appealing animal for studies of the physiology of learning?

a. Its axon is thicker than that of mammals and therefore easier to study.

b. Unlike mammals, it uses only one neurotransmitter and two types of receptors.

c. Compared to other invertebrates, it learns faster and remembers longer.

d. It has relatively few neurons, and they are the same from one individual to another.