a b c d

b

$R = \frac{mv}{qB} = \frac{\sqrt {2mE}}{qB}$ $ R_p =  \frac{\sqrt {2m_pE}}{eB}$ $ R_\alpha =  \frac{\sqrt {2(4m_p)E}}{2eB} = \frac{\sqrt {2m_pE}}{eB} = R_p$ $ R_d =  \frac{\sqrt {2(2m_p)E}}{eB} = \frac{\sqrt {4m_pE}}{eB} > R_p$ $\Rightarrow R_p = R_\alpha < R_d$