Why Do the Rings of Saturn Alternately Appear Very Distinct

Why do the rings of Saturn alternately appear very distinct and then almost disappear when viewed from Earth over periods of a few years?

A) Earth is much closer to Saturn at opposition than at conjunction;hence,the rings are more easily seen at this time.
B) The solar wind occasionally blows away the ring particles when the Sun is particularly active.
C) The ice crystals from which they are made melt and refreeze as the planet approaches and recedes from the Sun.
D) The plane of the rings is tilted with respect to the ecliptic plane and thus appear edge-on at times.