Because the population is denser there and the automobile is therefore inefficient as a means of transportation, a commuter rail system serving a given population is usually five times more efficient in a European city than it is in an American city.


serving a given population is usually five times more efficient in a European city than it is in an American city


serving a given population will usually be five times more efficient if it is placed in a European city instead of an American city


will usually be five times more efficient in a European city than one serving a comparable population in an American city


in a European city will usually be five times more efficient than will a system serving a comparable population in an American city


that is implemented in a European city will usually be five times more efficient than if it is implemented with a comparable population in an American city

OA - D Please explain.