The correct answer is A: Increase keying waveform rise and fall times. The most common method of reducing key clicks is to increase the keying waveform rise and fall times. Longer rise/fall times create smoother transitions that don't generate wide-bandwidth noise. Key clicks are caused by sharp transitions (short rise/fall times) that create high-frequency components. By increasing the rise and fall times, the transitions become smoother (more gradual), eliminating the high-frequency components that cause key clicks. This is typically done with a keying waveform shaper circuit that slows down the transitions. Most modern transceivers have adjustable keying speed or built-in keying filters that increase rise/fall times to prevent key clicks.