Answer is Option B i.e. Telegraphy
Frequency-shift keying (FSK) allows digital information to be transmitted by changes or shifts in the frequency of a carrier signal, most commonly an analog carrier sine wave. There are two binary states in a signal, zero (0) and one (1), each of which is represented by an analog wave form. This binary data is converted by a modem into an FSK signal, which can be transmitted via telephone lines, fiber optics or wireless media.