单项选择题
Behavioral psychologists apprehend that conditioned fear responses to atone previously paired with a shock diminish, if the tone is repeatedly presented without the shock, a process known as extinction. Since Parlor it has been hypothesized that this extinction does not erase conditioning, but forms a new memory. Research has now demonstrated that destruction of the infralimbic cortice blocks recall of fear extinction, indicating that it might store long-term extinction memory. Infralimbic neurons recorded during fear conditioning and extinction fire to the tone only when rats are recalling extinction on the following day, and rats indicating the least fear responses also demonstrate the greatest increase in infralimbic tone responses. Conditioned tones paired with brief electrical stimulation of infralimbic cortex elicit low fear responses in rats that have not undergone extinction. Thus, stimulation resembling extinction-induced infralimbic tone responses is able to simulate extinction memory.
According to the passage, "infralimbic neurons... fire to the tone only when rats are recalling extinction on the following day" (lines 7-9) for which of the following reasons（） A．Extinction has not been proven to erase the memory of fear conditioning in rats.
B．The extinction response requires a number of days to develop.
C．The subject’’s original fear response was not conditioned to a tone.
D．The infralimbic cortices carry the memory of fear extinction.
E．Rats that show the least fear demonstrate the greatest increase in infralimbic tone responses.