How were the rings of Uranus discovered?

A. by William Herschel, while he also found the two largest moons
B. by Percival Lowell, who observed two "bumps" on either side of Uranus
C. photometric observations of the occultation of a star made from Earth
D. by the Hubble Space Telescope in the infrared
E. by Voyager 2 when it passed by Uranus in 1986