The westinghouse air brake, first demonstrated successfully in 1868, had been developed to such an extent by 1887 that a train of 50 freight cars traveling at 20 miles per hour could be brought to a standstill in the space of 171 feet, whereas before they required 5 hand breakers over a distance of 1,500 feet for such a train to be stopped.
(a) whereas before they required 5 hand breakers over a distance of 1,500 feet for such a train to be stopped.(b) whereas previously 5 hand breakers operating over a distance of 1,500 feet had been required to stop such a train.(c) but before stopping the train required 5 hand breakers operating over a distance of 1,500 feet.(d) but previously they required 5 hand breakers over a distance of 1,500 feet stopping the train.(e) but before stopping such a train required 5 hand breakers over a distance of 1,500 feet.