在接触网导线距轨面高度小于（）的线路上，禁止登上敞车手闸台。
A. 6200mm
B. 6300mm
C. 6400mm
D. 6500mm
通讯是以叙述、描写为主要表达方式，迅速、具体、生动地反映现实生活的新闻体裁。
A. 正确
B. 错误
电动机最经济、最节能的办法是：使其在额定容量的75%～100%下运行，提高自然功率因数。
A. 正确
B. 错误
The reason why more and more of the large merchant vessels are being powered by medium-speed diesel engines is （）.
A. they operate between 150 and 450 rpm
B. they are connected to the propeller by gearing
C. their smaller size and weight
D. they can be connected directly to the propeller without gearing
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