E7H19 (C) 
Why is a phase-locked loop often used as part of a variable frequency synthesizer for receivers and transmitters?
A. It generates FM sidebands
B. It eliminates the need for a voltage controlled oscillator
C. It makes it possible for a VFO to have the same degree of stability as a crystal oscillator
D. It can be used to generate or demodulate SSB signals by quadrature phase synchronization
