Problem $17.$ A deuteron is moving with a speed of $2\mathrm{.}0{10}^6\frac{m}{s}$ at right angles to a magnetic field. The field is uniform, with magnitude $B=0\mathrm{.}40T.$ The mass and charge of a deuteron are $3\mathrm{.}3{10}^{-27}kg$ and $1\mathrm{.}6{10}^{-19}C,$ respectively. The radius of the deuteron orbit is approximately

a$.10$ cm

b$.27$ cm

c$.1\mathrm{.}8$ cm

d$.21$ cm

e$.6\mathrm{.}3$ cm