[单选题]
A nuclear reaction is said to be endothxt-ust9r 1ns 50ku ripdu(+9 ber( ce w6t 8n 6uuwb,f-mxpm6o ohu36amx;su9 z9mic if the total kinetic energy is
A. less after the reaction than before.
B. equal both before and after the reaction.
C. greater after the reaction than before.
D. zero after the reaction.