What happened at point C to end with D?
a
A transferred thermal energy to B to equalize both in D. Warmer always moves toward colder areas.
b
The surrounding air transferred thermal energy to A and B to equalize both in D. Air is the best conductor of heat.
c
B transferred thermal energy to A to equalize both in D. Cold always moves toward warmer areas.
d
This scenario can only be possible in a controlled setting in lab.