Which statement$($s$)$ is$($are$)$ correct about ASK and PSK signaling?

$($A$)$ ASK modulates the message by varying the waveform$$s amplitude and PSK modulates

the message by varying the waveform$$s phase.

$($B$)$ PSK signaling has constant amplitude.

$($C$)$ Both $($A$)$ and $($B$)$ are correct.

$($D$)$ None of the above.