Concept:Rail transport operates on fixed routes and fixed schedules, which reduces its ability to adapt to individual needs.Explanation:Railways cannot change their routes or departure times easily.They serve only the places where tracks are laid.They do not provide door-to-door service, unlike road transport.This lack of flexibility makes it difficult to meet special or urgent requirements of customers.Therefore, among the given options, the main disadvantage is that rail transport is not flexible.Answer:C. it is not flexible