One feature common to both the Debye theory and the Einstein theory of the specific heat of a crystal composed of Nidentical atoms is that the A. Average energy of each atom is 3kT B. Vibrational energy of the crystal is equivalent to the energy of 3N independent harmonic oscillators C. Crystal is assumed to be continuous for all elastic waves D. Speed of the longitudinal elastic waves is less than the speed of the transverse elastic waves E. Upper cutoff frequency of the elastic waves is the same