Concept:Igneous and sedimentary rocks are classified mainly by how they form and what they look like.Explanation:Igneous rocks form from the cooling and solidification of magma or lava.Sedimentary rocks form from the compaction and cementation of sediments or organic materials.These differences in origin also produce clear differences in appearance, such as crystalline texture in igneous rocks versus layered or grainy texture in sedimentary rocks.Thus, the key distinguishing features are appearance and origin.Answer:A. appearance and origin