Which of the following best expresses the main idea of the passage
A． Though the forces which influence GRBs are now established, scientists have yet to establish their cause. B． Scientists have now established the role that kinetic energy plays in the existence of GRBs. C． Certain aspects of GRBs have finally allowed scientists to link them to specific kinds of collapsed stars. D． Though still perplexed by the cause of GRBs, scientists have discovered how they manage to escape the gravity of black holes. E． Fireballs can transform explosive energy into observed radiation, as had long been hypothesized.