A proton, a deuteron and an `alpha`- particle having the same kinetic energy are moving in circular trajectors in a constant magnetic field. If `r_p, r_d` and `r_(alpha)` denote respectively the radii of the trajectories of these particles then
A. `r_(alpha)=r_(p)ltr_(d)`
B. `r_(alpha)gtr_(d)gtr_(p)`
C. `r_(alpha)=r_(d)gtr_(p)`
D. `r_(p)=r_(d)=r_(alpha)`
