【单选题】

According to the passage, the fireball which emits the initial GRBs differs from the stage in which it produces aftershocks in that
A．(A) the former lacks the accelerated velocity of the latter

B．(B) the former is easier to observe than the latter
C．(C) the former has higher photon density than the latter
D．(D) the former contains a greater number of positrons than the latter
E．(E) the former is in a state of expansion while the latter is in a state of contraction