Which key on the phone should be pressed and held when plugging in the phone power to start the 7800 or 8800 series IP phone reset process?

Cisco provides a factory reset option on every IP phone model ‘or phone recovery and troubleshooting. Which key on the phone should be pressed and held when plugging in the phone power to start the 7800 or 8800 series IP phone reset process?
A. # key
B. Programmable feature button
C. Settings button
D. * key