What is the CNO cycle?

Question

 What is the CNO cycle? 

 Answers:  

• the process by which helium is fused into carbon, nitrogen, and oxygen 
• the process by which carbon is fused into nitrogen and oxygen 
• a type of hydrogen fusion that uses carbon, nitrogen, and oxygen atoms as catalysts (Correct Answer)
• the period of a massive star's life when carbon, nitrogen, and oxygen are fusing in different shells outside the core 
• the period of a low-mass star's life when it can no longer fuse carbon, nitrogen, and oxygen in its core