Which of the following would be an example of a referendum?

a. A vote on who will serve on the Los Angeles city council.
b. A vote on whether recreational marijuana usage should be legalized in the state of California.
c. A vote on whether the governor of the state of Wisconsin should be recalled from office.
d. A vote on whether to overturn a law passed by the New York state legislature and signed by the governor of New York that imposes higher taxes on wealthy residents