Answer:
d. Hydrogen fusing into helium
Explanation:
When stars like sun burn their nuclear fuel, they become white draft. They fuse hydrogen cores into helium. This fusion produces heat and pressure in the outward direction. But, this pressure is balanced due to the gravity of star’s mass. In this way, planetary nebula is created. The major benefit of white draft is that they warm enough planets to keep water in liquid state on their surface.
