Concept:A source of energy is a material that releases usable heat or power when burned, and coal is a fossil fuel rock.
Explanation:The correct rock is the one that can be used as fuel.
Sandstone and granite are ordinary rock types with no fuel value.
Graphite is a form of carbon used in pencils and lubricants, not as a fuel.
Coal is a sedimentary rock formed from decomposed plant matter over millions of years.
When coal burns, it releases heat energy that can generate electricity and power machinery.
Therefore, coal is the direct source of energy among the options listed.
Answer:B. Coal