Marginal user cost----The user cost of the last unit of resource.

边际使用者成本——使用者最后一单位资源成本。

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That is, the marginal cost of an additional user is essentially zero for a sizeable number of users, but then marginal cost grows rapidly in the number of users.

这样，在一定人数内，新增一个消费者的边际成本基本为零，但是当使用者达到一定人数后，新增一个消费者的边际成本将非常明显。

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