Explanation: A sample-and-hold circuit accurately captures an instantaneous analog voltage and stores it for a period. The core components are: 1. **Analog Switch:** To "sample" the input voltage by momentarily connecting it to the storage element. 2. **Capacitor:** To "hold" the sampled voltage as a charge. 3. **Input Buffer (Amplifier):** An op-amp voltage follower at the input ensures the capacitor charges quickly and accurately without loading the input signal source. 4. **Output Buffer (Amplifier):** Another op-amp voltage follower at the output provides a low-impedance output and prevents the load from discharging the capacitor, maintaining the held voltage. Option D correctly identifies all these essential components for a functional and practical basic sample-and-hold circuit. Options A, B, and C are incomplete, missing critical elements like the capacitor for storage or the necessary input/output buffers for proper operation and isolation.