Limestone is a sedimentary rock.
Sedimentary rocks are formed by the accumulation and consolidation of sediments, which are small particles of rock, soil, and other materials that are transported and deposited by wind, water, or ice. Limestone is a type of sedimentary rock that is formed from the accumulation of the remains of marine organisms, such as shells and coral, as well as other calcium-rich materials.
Gabbro and granite, on the other hand, are both igneous rocks, which are formed from the cooling and solidification of magma or lava. Marble is a metamorphic rock, which is formed from the recrystallization of limestone or other sedimentary rocks under high pressure and temperature.
Therefore, of the rocks listed, limestone is the only sedimentary rock. The others are igneous or metamorphic rocks.