这是全球农业的储备系统。
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。
He said he was lucky the airport had a back-up system of its own generators 'u2014 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。