[单选题]
A cyclotron of radius 0.25 m acceleratdxi5 m 8th7zdj3n gf)(es3su wfzi t9.5i protons in a 1.7-T magnetic field. What is the frequency for the applied alternatif5iz3tw.9u is ng voltage?
A. $0.26 \; MHz$
B. $2.6 \; MHz$
C. $26 \; MHz$
D. $260 \; MHz$
