Described how synchronized oscillations are produced?

Which of the following correctly described how synchronized oscillations are produced?

a. A central pacemaker must be present to produce a synchronous rhythm in a set of neurons.

b. In a set of neurons, each individual will take turns to direct other neurons.

c. A central pacemaker directs the activity of a set of neurons.

d. Rhythm from a central pacemaker is transferred to a secondary pacemaker, which will direct the activity of a set of neurons.