An administrator has configured a strict RPF check on FortiGate. How does strict RPF check work?

An administrator has configured a strict RPF check on FortiGate.
How does strict RPF check work?

A. Strict RPF allows packets back to sources with all active routes. B. Strict RPF checks the best route back to the source using the incoming interface. C. Strict RPF checks only for the existence of at least one active route back to the source using the incoming interface. D. Strict RPF check is run on the first sent and reply packet of any new session.