Read the excerpt from "elevator systems of the eiffel tower, 1889" by robert m. vogel. the first complete elevator machine in the united states, constructed in 1855, was a complex and inefficient contrivance built around an oscillating-cylinder steam engine. the advantages of an elevator system independent of the mill drive quickly became apparent, and by 1860 improved steam elevator machines were being produced in some quantity, but almost exclusively for freight service. it is not clear when the first elevator was installed explicitly for passenger service, but it was probably in 1857, when otis placed one in a store on broadway at broome street in new york. in the decade following the civil war, tall buildings had just begun to emerge; and, although the skylines of the world’s great cities were still dominated by church spires, there was increasing activity in the development of elevator apparatus adapted to the transportation of people as well as of merchandise. operators of hotels and stores gradually became aware of the commercial advantages to be gained by elevating their patrons even one or two floors above the ground, by machinery. the steam engine formed the foundation of the early elevator industry, but as building heights increased it was gradually replaced by hydraulic, and ultimately by electrical, systems. which statement correctly describes the order of events in the development of elevators? a. because hotel and store operators became aware of the commercial advantages of elevating their patrons by machinery, otis placed an elevator in a store on broadway at broome street in new york. b. after the first elevator was installed for passenger service, hotel and store operators became aware of the commercial advantages of elevating their patrons by machinery. c. when hotel and store operators became aware of the commercial advantages of elevating their patrons by machinery, the steam engine formed the foundation of the early elevator industry. d. as building heights increased, the steam elevator was replaced by hydraulic and electrical systems, and hotel and store operators became aware of the commercial advantages of elevating their patrons by machinery.