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.)
-(c) Two electrons with equal speeds, one moving east and one moving west, collide. After the collision, the electrons move north and south with smaller speeds than they had originally. Nothing else is emitted.

A) C
B) $F$