What Factor Listed Below Did Not Lead Pavlov to Determine

What factor listed below did not lead Pavlov to determine that an extinguished conditioned response was not erased or forgotten, but only inhibited?

A) The conditioned stimulus still appears to create an orienting reflex.
B) The conditioned response could be recovered less time than was originally required to learn it.
C) The neutral stimulus was no longer neutral.
D) Brain scansdicated that a permanent change at the synapses had occurred