Concept:Organically formed rocks are sedimentary rocks built from the remains of living organisms.Explanation:Coal forms from the compressed remains of ancient plants over millions of years.Grit is a clastic sedimentary rock made of sand-sized grains.Shale is also clastic, formed from compacted mud and clay particles.Gypsum is a chemical sedimentary rock formed by evaporation of water rich in minerals.Therefore, coal is the only rock in the list that is organically formed.Answer:A. coal