The correct answer is option 1.Distributed systems are using fixed routing whereas dynamic and virtual routing is not used in the distributed system.Fixed routing: A path from A to B is specified in advance; the path changes only if a hardware failure disables it. Since the shortest path is usually chosen, communication costs are minimized. Fixed routing can not adapt to load changes.Ensures that messages will be delivered in the order in which they were sent.Virtual routing: A path from A to B is fixed for the duration of one session.Different sessions involving messages from A to B may have different pathsA partial remedy to adapting to load changesEnsures that messages will be delivered in the order in which they were sentDynamic routing: The path used to send a message from site A to site B is chosen only when a message is sent. Usually, a site sends a message to another site on the link least used at that particular timeAdapts to load changes by avoiding routing messages on heavily used pathMessages may arrive out of orderHence the correct answer is (a) only.