Complete the sentence.
A fossil is ().
a body part of a living organism the preserved remains of an ancient organism a model of an organism made by humans
Fossils are preserved remains of the body parts or activities of ancient organisms.
Some fossils show the body parts of organisms. Bones and shells are two body parts that are commonly preserved in fossils.
Some fossils show traces of an organism's activities. Footprints and burrows are two examples of traces that can be preserved in fossils. A burrow is a hole dug by an animal.
All fossils are formed in nature. They take thousands of years to form.