Answer: option 3. hollow forms are left in sediment by decaying organisms.
Explanation: Fossils usually form when sediment buries a dead organism. As sediment piles up, the organism's remains are subjected to pressure and heat. These conditions force gases and liquids from the body. A thin film of carbon residue is left, forming a silhouette of the original organism called a carbon film.
i’m not fully confident in this answer though :/
