What is "frequency modulation" (FM)?

A) Varying the amplitude of a carrier signal

B) Varying the frequency of a carrier signal based on the modulating signal

C) Keeping the frequency constant while changing the amplitude

D) Filtering a signal to enhance clarity

Answer: B) Varying the frequency of a carrier signal based on the modulating signal

Explanation: Frequency modulation (FM) involves changing the frequency of a carrier signal in accordance with the amplitude of the input modulating signal, widely used in radio broadcasting.