There is a supplementary water supply in case the main supply fails.

万一主水源断了，我们另外有供水的地方。

youdao

The Company closed the main supply monitoring, surveillance cameras, monitoring equipment, hard disk recorders, network cameras, smart ball, ball speed, infrared cameras, micro-cameras and so on.

本公司主要供应闭路监控，监控摄像机，监控器材，硬盘录像机，网络摄像机，智能球，高速球，红外摄像机，微型摄像机等。

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By eighteen-sixty-two, the trail was the main supply line for Union forces in the Southwest.

VOA: special.2009.03.30

The main supply of cargoes for this comes from Ex-Im Bank-financed lending to buyers of US goods.

FORBES: Intermarine Executives Discuss Ship Financing, Piracy, and Global Maritime Trade

The majority came from the poorest parts of Europe - Moldova, Romania and Ukraine - but the main supply route is through Serbia.

BBC: 'Slave trade' thrives in Bosnia

The country's main supply route, a railway connecting Brazzaville and Pointe Noire, the oil-producing town, has been disrupted for the past seven months.

ECONOMIST: Congo-Brazzaville