Answer :
Fossils are made by the imprints of hard materials that do not decompose quickly. Organs would not be found in fossils as they begin decomposing very shortly after the animal's death, way before a fossil will begin to form. However, the teeth, along with the bones, would remain, and be found in fossils.
Letter D would be your answer because the other options decompose. Depending on the environment and other factors such as temperature and water some body parts decompose more quickly than others. Hard material like bones and teeth usually take a long time to decompose. Hopefully this helps somewhat.
