What Process Maintains the Encke Gap in Saturn's Rings

What process maintains the Encke gap in Saturn's rings?

A) The gap is simply the space between the A ring and an outer ring that formed from the breakup of a small satellite.
B) One of Saturn's satellites orbits Saturn twice for every 3 times that a particle in the gap would orbit, and exerts a resonant pull that clears the gap of particles.
C) A gravitational disturbance by Titan, Saturn's largest satellite, creates waves in the A ring, which sweep the region immediately outside the A ring clear of particles.
D) A small moon orbits within the gap and shepherds particles outward and inward away from the middle of the gap.