What Does the Phenomenon of Spontaneous Recovery Suggest

What does the phenomenon of spontaneous recovery suggest?

A) When a conditioned response is extinguished, higher-order responses replace the original response.
B) Classical conditioning can be used only to condition biologically meaningful responses.
C) Once a conditioned response has been extinguished, a person will also stop responding to other stimuli that are similar.
D) Even if a person is able to extinguish a conditioned response, there is an excellent chance that it will reappear later.