[单选题]
A generator coil rotato9 9 -i fyhciq1aazg6cz-,*ures through 60 rev+x7pbiuo;fq q c w5u;i11e:xrolutions each second. The frequency of the; p+q1:e1 bur xowiq i5u7xf;c $emf$ is
A. 30 Hz.
B. 60 Hz.
C. 120 Hz.
D. cannot be determined from the information given.
