The diagram shows the tracks from an event at point P in a bubble chamber. There is a
uniform magnetic field directed into the page.
Which of the following is the reason why the tracks shown cannot represent the
production of a proton-antiproton pair with equal kinetic energies?
A The curvature is perpendicular to the magnetic field.
B The tracks curve in different directions.
C The tracks have different curvatures.
D There is no track before point P.