A Planetary Nebula Is a

A planetary nebula is a

A) gas shell, the atmosphere of a red giant star, slowly expanding away from the core of the star.
B) contracting spherical cloud of gas surrounding a newly formed star in which planets are forming.
C) nebula caused by the supernova explosion of a massive star.
D) disk-shaped nebula of dust and gas rotating around a relatively young star in which planets will eventually form.