The superficial epithelia cells do not bind the active ingredient and thus only serve as a transit area.

浅表的上皮细胞并不与活性药物成分结合，因而只是运输区。

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Washington's public transit operator, the Metropolitan Area Transit Authority, increased the number of uniformed officers patrolling the system, said Metro spokeswoman Lisa Farbstein.

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He called it the deadliest crash in the history of the Washington Metropolitan Area Transit Authority, known as Metro.

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The Washington Metropolitan Area Transit Authority said it would restore limited rail service.

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