Answer the following question given this paragraph: 

Most sedimentary rocks form from sediments. Sediments are small pieces of other rocks, like pebbles, sand, silt, and clay. Sedimentary rocks may include fossils. Fossils are materials left behind by once-living organisms. Fossils can be pieces of the organism, like bones. They can also be traces of the organism, like footprints.


Q: What is the term for something left behind by once-living organisms?

 Choices:

- decay

- waste matter

- deposits

- fossils

A:
fossils
