Which of the following most logically completes the passage?
A business analysis of the Appenian railroad system divided its long-distance passenger routes into two categories: rural routes and interurban routes. The analysis found that, unlike the interurban routes, few rural routes carried a high enough passenger volume to be profitable. Closing unprofitable rural routes,however, will not necessarily enhance the profitability of the whole system, since ________.
a large part of the passenger volume on interurban routes is accounted for by passengers who begin or end their journeys on rural routes
within the last two decades several of the least used rural routes have been closed and their passenger services have been replaced by buses
the rural routes were all originally constructed at least one hundred years ago, whereas some of the interurban routes were constructed recently for new high-speed express trains
not all of Appenia's large cities are equally well served by interurban railroad services
the greatest passenger volume, relative to the routes' capacity, is not on either category of long-distance routes but is on suburban commuter routes