From Where Does Titan's Thick, Nitrogen-Rich Atmosphere Likely Arise

Multiple Choice

From where does Titan's thick, nitrogen-rich atmosphere likely arise?

A) photodissociation of methane and ammonia in its atmosphere
B) emitted by frequent volcanic eruptions
C) deposited by ongoing cometary impacts over the age of the Solar System
D) photosynthesis of algae in oceans that lie beneath its icy surface
E) released from underground reservoirs from early impacts.