The correct answer to this question is A, Comet. They are small, icy solar system bodies. This is until the pass close to the Sun and warms up. When this occurs, the outgassing process starts, which is the comet releasing gas. Comets contain a nucleus, which is the body, as well as water, other ices, and nitrogen.
Perihelion is the point in the comet that gets closest to the Sun. The aphelion is the furthest away. If a comet orbits the Sun too many times, it will break apart. Most comets are formed in the solar system regions Oort Cloud and Kuiper Belts.