Several of these flow into a branch sewer, which joins first a sub-main and then a main sewer taking it to the treatment plant.

这些街道污水管又相结一条污水支管。此支管与次干管连接，然后经主干管将污水送至污水处理厂。

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The advantage of using sub models is that they can exist independently of the main model.

使用子模型的优势在于它可以独立地存在主模型。

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Processes (main process, sub process, services, tasks)

流程（主要的流程、子流程、服务、任务）

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Adversarial relationships between customers, main contractors and sub-contractors mean that design changes often cause rows and that problems are not tackled until they reach crisis proportions.

ECONOMIST: Are British builders uniquely awful?

Work to expand the refinery was sub-contracted by Total's main contractor - engineering firm Jacobs - to an Italian company, IREM, which decided to use its own foreign workforce.

BBC: Foreign labour row 'deal reached'

In some countries in sub-Saharan Africa, traditional apprenticeships are the main type of skills training for those not formally employed.

UNESCO: One third of young people in Sub-Saharan Africa fail to complete primary school and lack skills for work | United Nations Educational, Scientific and Cultural Organization