**Explanation:**

In order to determine which of the given circuits employ feedback, let's first understand what feedback is.

**Feedback** is a technique used in electronic circuits to control and improve the performance of the circuit. It involves taking a portion of the output signal and feeding it back to the input of the circuit. This feedback signal can be in-phase or out-of-phase with the input signal and can be used to control various aspects of the circuit's behavior, such as gain, stability, distortion, etc.

Now, let's analyze each of the given circuits and determine if they employ feedback:

1. **Oscillator**: An oscillator is a circuit that generates a continuous waveform at a specific frequency. It typically employs positive feedback to sustain oscillations. The output signal is fed back to the input to reinforce and maintain the oscillations. Therefore, the oscillator circuit employs feedback.

2. **Emitter follower**: An emitter follower is a common type of transistor amplifier circuit. It has a high input impedance and a low output impedance, making it suitable for impedance matching and buffering applications. However, the emitter follower does not employ feedback. The output signal is not fed back to the input, and there is no signal processing that affects the input signal.

3. **Power amplifier**: A power amplifier is a circuit that amplifies the power level of an input signal to drive a load, such as a loudspeaker or motor. Power amplifiers can employ both negative and positive feedback techniques to improve their performance. Negative feedback is often used to reduce distortion and improve linearity, while positive feedback can be used to increase gain or stability. Therefore, the power amplifier circuit can employ feedback.

Based on the analysis above, we can conclude that **only the oscillator and power amplifier circuits employ feedback**. Therefore, the correct answer is option **D) 1, 2, and 3**.

Oscillator