A, proton, a deuteron and `alpha`- an particle having the same kinetic energy are moving in circular trajectories in a constant magnetic field. If `r_ p` , `r_d` and denote respectively the radii of trajectories of these particles, then
Options:
(a) `r_alpha=r_p < r_d`
(b) `r_alpha>r_d > r_p`
(c) `r_alpha=r_d > r_p`
(d) `r_p=r_d=r_alpha`