A. Modulo-demolo
B. Modulation – demodulation
C. Modulator – demodulator
D. Modulation-demodulating

Solution

C. Modulator – demodulator

Explanation

The word "modem" stands for "modulator-demodulator". A modem's purpose is to convert digital information to analog signals (modulation), and to convert analog signals back into useful digital information (demodulation).