Answer:
c)Tidal forces from the planet prevent them from accreting.
Step-by-step explanation:
According to the Roche limit and Hill spheres limit Saturn's rings are too close to the planet. This causes the tidal forces to tear the particles i.e., accretion will not start.
This can be even noticed in the rings itself. The C ring of Saturn which is closer to the planet has unclumped particles while in the B ring you can observe clumping.