An electron, a proton, a deuteron and an alpha particle, each having  speed v, are in a region of constant magnetic . field perpendicular to the direction of the velocities of the particles. The radius of the circular orbits of these particles are respectively R_e, R_p, R_d and $R_{\alpha }$. It follows that

• A

  R_e = R_p

• B

  R_p = R_d

• C

  ${\mathrm{R}}_{\mathrm{d}}={\mathrm{R}}_{\mathrm{\alpha }}$

• D

  ${\mathrm{R}}_{\mathrm{p}}={\mathrm{R}}_{\mathrm{\alpha }}$