题目内容
Sometimes there is only one single rail for the train to run, which is called ____.
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A cog rail or a rack rail is a railway with a ________rack rail, usually between the running rails.
The trains are fitted with one or more cog wheels or ______ that mesh with this rack rail.
The rack rail is used to make the trains to run on a ________ _________.
The special equipment of the subway line includes track equipment, including mainly steel track, contact rail, _______,________, ___________and connecting parts, all of which together consititute the ________of the operation of subway trains.
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