The correct answer is: A. Source of raw material and export centers.
The British developed the Indian railway system to facilitate the transportation of raw materials from the interior of India to the ports on the coast, from where they could be shipped to Britain. This was essential for the British economy, as India was a major supplier of raw materials such as cotton, tea, and jute.
Option B is incorrect because the British were not interested in developing Indian production centers. They wanted to extract raw materials from India and ship them back to Britain, where they would be processed and manufactured.
Option C is incorrect because the British were not interested in developing Indian markets. They wanted to sell their manufactured goods in India, but they did not want to buy Indian goods.
Option D is incorrect because the British were not interested in developing Indian infrastructure. They were only interested in developing the railway system to the extent that it would facilitate the transportation of raw materials from India to Britain.