[单选题]
A cyclotron of radiuskx5 ht5r0 9gp)lh o2am 0.25 m accelerates prq*t.m :bavq+bklc fu yy/-f*/otons in a 1.7-T magnetic field. What is the kinetic energy of the protons whenuflaty*/b cyv: -mq/b .k f*+q they leave the cyclotron?
A. $7.8 \; keV$
B. $8.7 \; keV$
C. $7.8 \; MeV$
D. $8.7 \; MeV$
