To these is the premise of the subway to have good air conditioning and ventilation system.

要实现这些的前提是地铁要有良好的空调通风系统。

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They stopped adding smell into the ventilation system of the subway train or of the car of the train months before.

这种在地铁通风系统、或者只是在某一节车厢的通风系统内添加臭味的行为几个月前才停止。

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