The correct answer is D. Bandwidth.
A channel parameter is a characteristic of a communication channel that affects the performance of a communication system. Coherence time, rms delay spread, and Doppler spread are all channel parameters. Bandwidth is not a channel parameter.
Coherence time is the time over which the channel impulse response remains essentially constant. It is a measure of how quickly the channel changes. Rms delay spread is the square root of the average of the squared delays of the multipath components in the channel. It is a measure of how spread out the multipath components are in time. Doppler spread is the spread of the Doppler frequencies of the multipath components in the channel. It is a measure of how fast the channel is changing.
Bandwidth is a measure of the range of frequencies that a channel can support. It is not a measure of how quickly the channel changes. Therefore, it is not a channel parameter.