Explanation: Frequency-shift keying (FSK) provides an advantage over on-off keying (OOK) by increasing the effective signal-to-noise ratio (SNR) at the receiver. In FSK, the transmitter is continuously emitting a signal, merely shifting its frequency between two states (e.g., "mark" and "space"). This contrasts with OOK, where the signal is either present or entirely absent. Because the FSK signal is always present, the receiver constantly has a carrier to process, allowing for more reliable detection and better rejection of noise. This continuous signal presence helps the receiver distinguish between the two signal frequencies rather than discerning a signal from the mere absence of a signal amidst noise, thus enhancing overall SNR and making FSK more robust in noisy conditions. * **A) Increase of transmitter bandwidth:** FSK generally requires *more* bandwidth than OOK for the same data rate, which is typically a trade-off, not an inherent advantage. * **B) Decrease of signal-to-noise ratio:** This is incorrect; FSK improves SNR performance.