challenge: What gauge was the Naupada-Gunupur branch line converted to in 2011?
  
  A. 4 ft 8.5 in (1,435 mm) standard gauge
  B. 5 ft 6 in (1,676 mm) broad gauge
  C. 2 ft 6 in (762 mm) narrow gauge
  D. 3 ft 6 in (1,067 mm) narrow gauge
  Answer: 