What are comets primarily composed of?

Comets are primarily composed of ice and rock, which is why the correct choice is this option. These celestial objects are often described as "dirty snowballs" because they consist primarily of frozen gases—such as water, carbon dioxide, ammonia, and methane—mixed with various types of rocky material and dust. As comets approach the Sun, the heat causes the ice to vaporize, creating a glowing coma (a cloud of gas and dust) around the nucleus and often a tail that points away from the Sun due to solar wind.

The combination of these materials is crucial in forming the unique structures and behavior of comets as they travel through the solar system. For instance, when they come close to the Sun, the sublimation of the ice results in the distinctive tails that are observed, further illustrating their icy composition.