Concept:Chalk is a biogenic sedimentary rock formed from the microscopic skeletons of marine organisms.
Explanation:Rocks are grouped by how they form.
Granite is an igneous rock from cooled magma.
Sandstone is a clastic sedimentary rock made of sand grains.
Slate is a metamorphic rock formed from shale under heat and pressure.
Chalk is a soft, white limestone composed mainly of the calcium carbonate skeletons of tiny sea plants, such as coccolithophores, and sea animals, such as foraminifera.
These organisms die and sink to the ocean floor, where their shells accumulate over millions of years.
Compaction and cementation turn these deposits into chalk.
So, chalk is the rock that matches the description exactly.
Answer:A. Chalk