The correct answer is: C. common base.
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 grounded. The output impedance of a transistor connected in common base configuration is the highest because the collector is connected directly to the power supply. This means that there is no resistance in series with the collector, which results in a high output impedance.
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 power supply. The output impedance of a transistor connected in common emitter configuration is lower than that of a common base configuration because there is a resistance in series with the collector. This resistance is called the collector load resistor, and it helps to reduce the output impedance of the transistor.
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 power supply. The output impedance of a transistor connected in common collector configuration is the lowest of the three configurations because there is no resistance in series with the emitter. This means that the output impedance of the transistor is equal to the resistance of the load connected to the emitter.
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