Concept:Sedimentary rocks are formed by the deposition and compaction of sediments over time.
Explanation:Limestone is a sedimentary rock formed from compressed shells and calcium carbonate remains.
Chalk is a soft, white variety of limestone, so it is also sedimentary.
Graphite is not a sedimentary rock; sandstone is sedimentary.
Gabbro is an igneous rock, while schist is a metamorphic rock.
Gneiss is metamorphic and granite is igneous, so they are not sedimentary rocks.
Therefore, the only pair containing two sedimentary rocks is limestone and chalk.
Answer:C. limestone and chalk