The correct answer is C. Mean excess delay.
The power delay profile (PDP) is a function of the delay and represents the power received at each delay. The RMS delay spread is the square root of the second moment of the PDP, which is a measure of the spread of the PDP. The Doppler spread is a measure of the spread of the frequency components of the received signal, which is caused by the relative motion of the transmitter and receiver. The mean excess delay is the average delay of the received signal, which is the first moment of the PDP.
The mean excess delay is not a multipath channel parameter that can be determined from the power delay profile because it is not a measure of the spread of the PDP. The mean excess delay is a measure of the average delay of the received signal, which is the first moment of the PDP. The RMS delay spread and Doppler spread are measures of the spread of the PDP, which are caused by the multipath propagation of the signal.