[单选题]
A cyclotron of radius 0.25 m accelerates protons ivyuv v3kk7kkb *q5s2h /5ebh6n a 1.7-T magnev:: ingk41w ;nrd) drief2ua,tic field. What is the kinetic energy of the protons when they leave theai2gi:r fu k:rve,d n; n4dw1) cyclotron?
A. $7.8 \; keV$
B. $8.7 \; keV$
C. $7.8 \; MeV$
D. $8.7 \; MeV$
