Answer:
D. They are the remnants of the outer planet's accretion
Step-by-step explanation:
Comets are small irregular shaped and sized icy bodies found in Kuiper belt and Oort cloud. These are the primordial debris. The comets are the remnants of the outer planets accretion disk. These are composed of rocks, dust, ice and frozen gases. The comets present in Kuiper belt are short period comets. Comets revolve around the sun in elliptical orbit.