The correct option is C gauge width
The Indian railways are classified based on the gauge width of the rails. They are three types, Broad gauge with a rail width of 1.676 metres that cover roughly 74% of the rail length in India. Metre gauge with a width of 1 metre covers about 21% of rail length in India. The remaining 5% goes to Narrow gauge with a width of 0.762/0.610 metres.