Which of the Following Processes Is Consistent with the Law $\mathrm{C}$

Multiple Choice

Which of the following processes is consistent with the law of conservation of four-momentum? (Answer $\mathrm{C}$ if it is consistent with the law; $F$ if it violates it.)
-(d) A spaceship of mass $2 m$ originally at rest burns some matter-antimatter fuel until the ship's mass is $m$ . The light energy ejected from the ship in this process has total energy $m$ as well.

A) C
B) $F$