【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.