What type of circuit is associated with generating a continuous oscillation without any external trigger?

The correct answer is associated with the astable circuit, which is specifically designed to generate a continuous oscillation without requiring any external trigger. In an astable multivibrator, the circuit will constantly switch between its two unstable states, producing a square wave output. This behavior is due to the arrangement of components in the circuit, such as resistors and capacitors, which govern the timing and frequency of the oscillation. The inherent feedback within the circuit allows it to oscillate indefinitely, making it ideal for applications like clock signals and tone generation.

In contrast, a monostable circuit can only output a single pulse in response to an external trigger and then returns to its stable state. A stable circuit typically signifies a condition where the system remains in a stable equilibrium without oscillation. Triggered circuits, depending on the context, usually refer to circuits that change state only when an external signal is applied. Therefore, the key differentiator for the astable circuit is its ability to produce continuous oscillations autonomously, which is why it is the correct choice.