Two charged particles traverse identical helical paths in a completely opposite sense in a uniform magnetic field `vec(B)=B_(0)hat(K)`

Options

A. They have equal z-components of momenta.
B. They must have equal charges.
C. They necessarily represent a particle-antiparticle pair.
D. the charge to mass ratio satisfy:`(e/m)_1+(e/m)_2=0`

Answer

D