How Often Would an Observer Standing on Pluto's Surface See

How often would an observer standing on Pluto's surface see the satellite Charon rise above the horizon each day?

A) once each 6-hour day as Pluto rotates on its axis
B) twice each 6-hour day because Charon is in a retrograde orbit
C) once every 2 days because Charon orbits in the same direction Pluto rotates but more slowly
D) never-Charon is a synchronous satellite with an orbital period exactly equal to Pluto's rotation period