Answer:
Sink is Option A: fossil fuels such as coal, oil, and gas.
Step-by-step explanation:
The given option B, which is a location for carbon dioxide storage is not a sink. Neither is a volcano, Option C, which is made of hot molten rock erupt from Earth's surface or atmosphere, Option D a sink.
Fossils fuels such as coal, oil and gas are sink. Coal forms are formed when dead plants sink to the bottoms of swamps. The organic matter slowly becomes peat which gradually becomes coal, after a lot of pressure is crated on it. The other kinds of fossil fuels, oil and natural gas, are not rocks. They are also formed when tiny creatures get buried deep inside and over years, sediments change organic mater into natural gas (given enough pressure on them).