【单选题】

The discussion of the means by which GHBs escape black holes that is offered in the second paragraph suggests that which of the following must be assumed if the conclusions described in lines 3 - 5 are to he validly drawn
A．(A) The light emissions from GHBs always degrade from gamma rays to x-rays to visible light and, finally, to radio waves.

B．(B) Particles in GHBs include not only photons but electrons and their antimatter counterpart, positrons.
C．(C) The expansion of a fireball as it moves away from the black hole lowers photon density.
D．(D) Shock waves almost always form at the boundary between the fireball and the external medium.
E．(E) The timescale by which we witness astronomical phenomenon is always ruled by the principles of relativity.