[单选题]
A cyclotron of radius 0.25 m accelerates protons i1 jezl 01uw s6jf q ;f1kc2qse7vqxo0+n a 1.7-T magnetic field. oa6fwwfwb d6b68s v l-o;/ s8b What is the kinetic energy of the pro6olo-6w bv8b8s sffb d ww6a/;tons when they leave the cyclotron?
A. $7.8 \; keV$
B. $8.7 \; keV$
C. $7.8 \; MeV$
D. $8.7 \; MeV$
