[单选题]
A cyclotron of radius 0.2 gndms 3o0ma 6pk)8rd.5 m5 t(nv** 2+ydu2ym nbojheq* a accelerates protons in a 1.7-T magnetic field. What is the kinetic energy of th2 qand5m**tu2j*y (bey+oh nve protons when they leave the cyclotron?
A. $7.8 \; keV$
B. $8.7 \; keV$
C. $7.8 \; MeV$
D. $8.7 \; MeV$
