The correct answer is C. common emitter.
In a common emitter configuration, the input signal is applied to the base, the output signal is taken from the collector, and the emitter is connected to the ground. This configuration has the highest voltage gain because the collector current is amplified by the transistor’s current gain, β.
In a common base configuration, the input signal is applied to the base, the output signal is taken from the collector, and the emitter is connected to the positive supply voltage. This configuration has a low voltage gain because the collector current is amplified by the transistor’s current gain, β, but the output signal is also divided by the transistor’s emitter resistance, Re.
In a common collector configuration, the input signal is applied to the base, the output signal is taken from the emitter, and the collector is connected to the ground. This configuration has a high current gain because the collector current is amplified by the transistor’s current gain, β, but the voltage gain is low because the output signal is also divided by the transistor’s collector resistance, Rc.