Which circuit is bistable?

A bistable circuit is an electronic circuit that has exactly two stable states, meaning it can be toggled into one state and will remain there indefinitely until triggered to change back. A flip-flop is the classic example of a bistable circuit and serves as the fundamental building block of digital memory. Other options like AND and OR gates are combinational logic gates; their outputs depend only on the immediate state of their inputs, meaning they do not hold or 'remember' a state. A bipolar amplifier is an analog component used to increase signal strength, not a digital circuit with stable resting states.