Explanation: An emitter-follower amplifier, also known as a common collector configuration, is designed primarily for impedance matching and buffering. Its key characteristics are a very high current gain, a voltage gain that is slightly less than unity (1), a high input impedance, and a low output impedance. * **D) More current gain than common emitter or common base:** This is correct. The emitter-follower's current gain can be very high, often exceeding that of a common emitter amplifier and significantly higher than the common base configuration, which has a current gain near unity. This high current gain allows it to drive low-impedance loads from high-impedance sources effectively. * **A) More voltage gain than common emitter or common base:** Incorrect. The emitter-follower provides virtually no voltage gain (it's slightly less than 1), unlike common emitter and common base amplifiers which offer significant voltage amplification. * **B) More power gain than common emitter or common base:** Incorrect. While it has high current gain, its low voltage gain means its overall power gain is moderate. Common emitter amplifiers typically offer the highest power gain due to both significant voltage and current gain. * **C) Lowest input impedance of the three amplifier configurations:** Incorrect. The emitter-follower is known for its *high* input impedance, which is crucial for its buffering application. The common base configuration typically has the lowest input impedance.