Final answer:
The phase-shift oscillator usually has three lead or lag circuits (option b).
Step-by-step explanation:
The phase-shift oscillator usually has three lead or lag circuits (option b).
A phase-shift oscillator is a type of oscillator that generates a stable sinusoidal output signal. It uses a network of three RC (Resistor-Capacitor) or RL (Resistor-Inductor) circuits to generate the phase shift required for oscillation.
By properly designing the values of resistors and capacitors or inductors in the circuit, a phase shift of 180 degrees (π radians) can be achieved. This phase shift causes positive feedback, sustaining the oscillation. Thus, the correct answer is option b - three lead or lag circuits.