The dispersion law for a certain type of wave motion is w = (ck+m) /2, where w is the angular frequency, k is the magnitude of the propagation vector, c and m are constants. The group velocity of these waves approaches A. Infinity as k o and zero as k B. Infinity as ko and c as k C. c as k o and zero as k D. Zero as ko and infinity as k E. Zero as k o and c as k