单项选择题 Since rail network is not as extensive as highway network in most countries and its limitation to fixed track facilities, as a result, railroads provide （） service.

单项选择题 In general, factors influencing transportation costs can be grouped into 2 major categories---product-related factors and market-related factors. Please find below, （）is not belong to the market-related factors.

单项选择题 As some countries attempt to shift away from natural gas or petroleum energy systems toward coal-based systems, the need for coal slurry(煤泥) will increase in these countries,（）transport mode will be the first choice for transfer this kind of product.