Cassini's Division in the Rings of Saturn Is Thought to Be

Cassini's division in the rings of Saturn is thought to be due to gravitational forces from the moon Mimas. The orbital period of Mimas is 22.6 hours. What is the orbital period of any particles that exist within Cassini's division?

A) 22.6 hours-Mimas moves within Cassini's division.
B) 7.5 hours-this is one-third of Mimas's period.
C) 45.2 hours-this is 2× Mimas's period.
D) 11.3 hours-this is one-half of Mimas's period.