$A$, proton, a deuteron and $a$ -an particle having the same kinetic energy are moving in circular trajectories in a constant magnetic field. If $\mathrm{r}_{\mathrm{p}} \mathrm{r}_{\mathrm{d}}$ and denote respectively the radii of trajectories of these particles, then
(a) $\mathrm{r}_{\alpha}=\mathrm{r}_{\mathrm{p}}<\mathrm{r}_{\mathrm{d}}$
(b) $\mathrm{r}_{\alpha}>\mathrm{r}_{\mathrm{d}}>\mathrm{r}_{\mathrm{p}}$
(c) $\mathrm{r}_{0}=\mathrm{r}_{\mathrm{d}}>\mathrm{r}_{n}$
(d) $\mathrm{r}_{n}=\mathrm{r}_{\mathrm{d}}=\mathrm{r}_{1}$