Because of such factors, engineers have worked on increasing the efficiency of elevators, resorting to double-decker cars to service and to transfer systems that ( ) express and local elevators,

　　A.strengthen

　　B.explore

　　C.enforce

　　D.deploy

　　【答案】A。A 项：加强、巩固;B 项：探索;C 项：实施、强制;D 项：配置、展开。句意：由于这些因素，工程师们一直致力于提高电梯的效率，求助于双层汽车来提供服务和运输系统，以加强特快和本地电梯。故本题正确答案选 A。