Which is the only railway in Rajasthan running on narrow gauge in the plains of the country, which was built by Ram Singh, the ruler of Dholpur princely state?

• A. Sarmathura, Dholpur, Badi, Tantapur
• B. Samdari, Bhildi
• C. Rajgarh, Luharu
• D. Dholpur, Agra