What Is the Basic Difference Between Comets and Asteroids

Multiple Choice

What is the basic difference between comets and asteroids?

A) Comets always move in open orbits around the Sun and hence visit the Sun only once in their lifetime, whereas asteroids move in closed orbits.
B) Comets always emit their own light, whereas asteroids only reflect sunlight.
C) Comets are spherical, whereas asteroids are mostly irregular in shape.
D) Comets are mostly composed of roughly equal mixtures of rocks and ices, whereas asteroids are mainly composed of rocks.