A wave moving with constant speed on a uniform string passes the point `x=0` with amplitude `A_0`, angular frequency `omega_0` and average rate of energy transfer `P_0`. As the wave travels down the string it gradually loses energy and at the point `x=l`, the average rate of energy transfer becomes`P_0`/2. At the point `x=l`. Angular frequency and amplitude are respectively:
A. doubling the frequency doubles the rate at which energy is carried along the string
B. if the amplitude were doubled, the rate at which energy is carried would be halved
C. if the amplitude were doubled, the rate at which energy is carried would be doubled
D. the rate at which energy is carried is directly proportional to the velocity of the wave.