Step 1: In the public sector the government owns most of the assets and it provides all the services; the purpose is not to earn profits but the welfare of the people. Step 2: Indian Railways is owned and run by the Government of India, so it is a public sector enterprise (the post office is another example). Step 3: Birla Cement, Tata Iron and Steel Company (TISCO) and Reliance Industries Limited are owned by private individuals or companies, so they belong to the private sector. Step 4: Hence the correct answer is Indian Railways - Option (D).