The phase response of a pass band waveform at the receiver is given by \phi(f)=-2 \pi a\left(f-f_{c}\right)-2 p \beta f where f_{ c } is the centre frequency, and a and b are positive constants. The actual signal propagation delay from the transmittance to receiver is

(a) \frac{a-\beta}{a+\beta}                                          (b) \frac{a \beta}{a+\beta}

(c) α                                                        (d) β