Select correct statements for FM position:A$.$ At takeoff, the FM position is updated to the runway threshold position as stored in the database, possibly corrected by the takeoff shift entered on PERF TO page if no GPS$.$B$.$ In flight, the FM position approaches the radio position or the GPS position at a rate depending upon the aircraft altitude.C$.$ The FM position update at takeoff is inhibited when GPS PRIMARY is active.D$.$ All are correct.