According to the passage, "infralimbic neurons … fire to the tone only when rats are recalling extinction on the following day" 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.