How were the rings of the planet Uranus discovered:

W) astronomers in 1977 noticed stars were occulted by Uranus before the planet passed in front of them and reappeared afterwards

X) the Magellan 1 space probe took pictures of them

Y) the Hubble space telescope detected them with its infrared detector

Z) the rings are made of gases with certain signatures revealed in absorption spectra
W) ASTRONOMERS IN 1977 NOTICED STARS WERE OCCULTED BY URANUS BEFORE THE PLANET PASSED IN FRONT OF THEM AND REAPPEARED AFTERWARDS