Ursula Is Afraid of Some Rodents, After She Was Bitten

Ursula is afraid of some rodents, after she was bitten by a rat. She is afraid of all rats, as well as mice and hamsters, but is not afraid of guinea pigs or gerbils. Ursula's responses best demonstrate that

A) stimulus generalization has occurred.
B) stimulus discrimination has occurred.
C) stimulus generalization occurs along a gradient.
D) stimulus discrimination is unpredictable.