Option B (Railways) is correct because the textbook explicitly states that 'Railways are the principal mode of transportation for freight and passengers in India.' The term 'principal' indicates that railways are the most important mode. The context further emphasizes that railways bind the economic life of the country, accelerate development of industry and agriculture, and have been a great integrating force for more than 150 years. While roadways have an edge in certain aspects like door-to-door service and construction ease, and roadways have preceded railways, the question specifically asks for the 'most important' mode, which the textbook clearly identifies as Railways.