Concept:Sedimentary rocks are formed by the compaction of sediments over time.Explanation:Limestone is formed when shells, coral, and marine debris accumulate and become compacted.This makes limestone a sedimentary rock.Gabbro and granite are igneous rocks because they form from cooling magma.Marble is a metamorphic rock because it forms when limestone changes under heat and pressure.Thus, the sedimentary rock is limestone.Answer:A. Limestone