Which one of the following is the appropriate reason for considering the Gondwana rocks as most important rock systems of India?

• A. More than 90% of limestone reserves of India are found in them.
• B. More than 90% of India's coal reserves are found in them.
• C. More than 90% of fertile black cotton soils are spread over them.
• D. None of the reasons given above is appropriate in this context.