The Narrowness of the Rings of Uranus and Neptune Is

Multiple Choice

The narrowness of the rings of Uranus and Neptune is believed to be caused by

A) gravitational interactions between ring particles.
B) a spiral density wave which confines them.
C) the magnetic field which holds them in place.
D) the smaller mass of Uranus and Neptune as compared to that of Saturn.
E) small shepherd moons that orbit near the rings.