在（2）的基础上，另外假定服务中心可以设定3个，一个主中心和两个分中心，要求分配的服务量之比为2：1：1，而且规定一个住宅只能由其中一家服务中心提供服务。如何选址并且给出每条路线上的运输量。

-In (2), based on a presumption service center can be set to three, one center and two sub-centers, the amount of the request for allocation of service ratio of 2: 1: 1, and the provisions of a residence by one of only a service center to provide services. How the site and give traffic on each route.

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