Consider the following UNESCO World Heritage Sites in India:
1. Darjeeling Himalayan Railway (DHR)
2. Nilgiri Mountain Railway (NMR)
3. Kalka-Shimla Railway
4. Chhatrapati Shivaji Maharaj Terminus (CSMT)
How many of the above are recognized as part of the "Mountain Railways of India" UNESCO World Heritage Site?
1
Only one
2
Only two
3
Only three
4
All four