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.)
-(b) Two identical particles with equal speeds, one moving east and one moving west, collide. After the collision, the same particles move north and south, respectively, with the same speeds that they had originally.

A) C
B) F