Why is the Aplysia such a popular animal for single-cell studies of learning?

    a.    Aplysia have greater learning abilities than other invertebrates.
    *b.    Individual cells identified in one animal can be recognized in another.
    c.    Aplysia have short-term learning but not long-term learning.
    d.    Aplysia have only two neurotransmitters, one excitatory and one inhibitory.