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.