How Is Nitrogen Thought to Have Become the Dominant Gas

Multiple Choice

How is nitrogen thought to have become the dominant gas in the atmosphere of the moon Titan, a satellite of Saturn?

A) from the breakup of ammonia by solar UV into nitrogen and hydrogen; the light hydrogen atoms are then lost to space
B) from outgassing through volcanic vents; nitrogen is the predominant gas from such vents
C) Nitrogen has been present from primordial times, when Titan first formed.
D) from the collision with the surface of Titan of comets rich in nitrogen in liquid and solid form