Final answer:
Asteroids differ from comets in composition; asteroids are rocky, while comets are predominantly icy. As they approach the Sun, the ices in comets vaporize, creating a visible atmosphere and tail, which asteroids lack.
Step-by-step explanation:
The correct answer to how asteroids differ from comets is: Asteroids are made of rocky material. Comets are made of icy material. This distinction is important as it leads to different behaviors when these celestial bodies approach the Sun. Comets, which are primarily composed of frozen water and other volatiles with some solid grains, develop a bright atmosphere or coma and often a tail because of the sublimation of their icy parts. In contrast, asteroids, being rocky or metallic and containing less volatile material, do not exhibit these spectacular features.
Asteroids often remain in the asteroid belt between Mars and Jupiter, while comets come from regions such as the Kuiper Belt and the Oort Cloud, well beyond Neptune. It's interesting to note that the composition of these bodies helps us understand the conditions of the early solar system, as many asteroids and comets are considered relatively unchanged since that time, acting like cosmic fossils.