【单选题】

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.