This is a back-up system for world agriculture.

这是全球农业的储备系统。

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The home's existing gas heater ACTS as a back-up system and provides additional heating when needed.

房子原来的燃气加热器作为一个后备系统，在需要的时候提供额外的采暖。

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He said he was lucky the airport had a back-up system of its own generators — otherwise he would have to try to land in total darkness.

这个飞行员谈到当天他准备降落的情景。他说，幸运的是，机场自己有后备的发电设备。否则，他得设法在黑暗里降落。

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It said clear, sterile water would be discharged and there would be a back-up system in case of error.

BBC: Aerial view of Treyarnon Bay

The report also lauds the land-based eLoran radio navigation system as a very worthy back-up technology.

BBC: UK 'over-reliant' on GPS signals, engineers warn

Although the system is designed to failover to a back-up switch, the failover did not function as previously tested.

BBC: Blackberry's message goes missing