求帮忙理解这句话的意思，是gmat pack2里遇到的！

alexanderwww · 发表于 2017-9-15 18:19:17

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.

正确的是b

金木木 · 发表于 2017-9-18 09:46:35

BEFORE是连词，因此后面必须接内容，排除ACE
另外，D当中they指代不明，是car吗？car-stopping the train.明显不是car所以不对
只剩下下B

[SC悬赏令] 求帮忙理解这句话的意思，是gmat pack2里遇到的！

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