In the illustration, the component VR1 on the A1 AMPLIFIER MODULE is _________. EL-0060 A. a zener diode to regulate the +9 volt power supply from common B. a variable resistor diode to control the output to terminal 9 that controls the input to terminal 10 C. a zener diode that regulates the voltage to terminal 9 at 6.6 volts DC D. a tunnel diode with a breakdown voltage of 6.6 Volts DC