Which of the following statements accurately describe primary and secondary modulation of solenoids in a WT transmission?

A) primary modulation controls on-time at a frequency of 63 Hz
B) secondary modulation maintains an optimal current flow at 7,812 Hz
C) primary modulation has a variable duty cycle
D) all of the above

All of the statements accurately describe aspects of primary and secondary modulation in solenoids within a World Transmission (WT) system. Primary modulation indeed controls on-time with a variable duty cycle, typically at a frequency around 63 Hz, while secondary modulation is aimed at maintaining optimal current flow, often at a much higher frequency, such as 7,812 Hz.