What is a supernova?

A. A supernova occurs when the moon collides with a planet. The material from the collision is exploded into space. It is very energy intense.
B. A supernova occurs when a red super giant star explodes. It occurs when an aging massive star is nearing the end of its life., A supernova expels much of a star's material into space and is very energy intensive.
C. A supernova occurs when a Jovian gas giant implodes from galactic cooling. It occurs when a Jovian gas giant is formed. It is a very energy intensive.
D. A supernova occurs when white dwarf star cools and implodes. It occurs when a new white dwarf is formed. It is very energy intensive.