What are comets primarily composed of?

Comets are primarily composed of frozen gases and dust, which is why the correct answer is C. They are often described as "dirty snowballs" or "icy bodies" because they contain significant amounts of ice, including water, carbon dioxide, ammonia, and methane, along with dust and other particulates. When comets approach the Sun, the heat causes these frozen gases to sublimate, creating a glowing coma and often developing a tail that can extend for millions of kilometers. This distinct feature is a result of their unique composition that allows them to exhibit such behavior when they come close to the Sun.

The other options do not accurately reflect the primary composition of comets. While hydrogen and oxygen are prevalent elements in the universe, they do not account for the structure of comets. Comets also do not possess a significant proportion of nitrogen or sodium, making those options less relevant. Additionally, while rock and metal are found in asteroids and some other celestial bodies, they do not represent the primary characteristics of a comet's structure. Thus, understanding the composition of comets helps clarify their behavior and appearance in space.