[单选题]
A generator coil rotates through 60 revolutions each second. The f.+weq4(*zl fllj8rw*ek b/h g: q1nwwre (aoyoaxm6r +iy,3k816rgoc vquency of the akyo36,ryog8(6 vom rx+ ica1$emf$ is
A. 30 Hz.
B. 60 Hz.
C. 120 Hz.
D. cannot be determined from the information given.
