Which of the following is an accurate statement?

a. dc generators produce current with a voltage that changes from positive to negative.
b. ac generators produce current that is pulsating, but always remains positive.
c. step-down voltage transformers have a different number of turns in the primary than in the secondary winding, so they change the incoming voltage to a higher voltage.
d. step-up voltage transformers have a lower number of turns in the primary than in the secondary winding