13. An electron and a positron move side by side, at the same velocity of 0.8c, in the same direction on thex-axis. Finally, these two particles merge together thus annihilate each other, and two photons aregenerate【複選題】 
(A) These two photons move in the same direction
(B) These two photons move in opposite direction with momentum p1 = 2.55 MeV/c, p2 = 0.51 MeV/c
(C) These two photons move off with the energy E1 = 1.533 MeV, E2 = 170.36 KeV
(D) These two photons move in the same direction, with the energy E1 = 1.55 MeV, E2 = 0.51 MeV
(E) These two photons move off, with the wavelength