n.后援；备份；备用
Liu Bei was given 1,000 troops as the back up force. 刘备带一千人马作后援。
You can back up and restore full-text catalogs. 可以备份和还原全文目录。
This option will back up files on the volume. 该选项将备份卷中的文件。
You should carry a spare wheel in the back of your car. 你应在车后带一个备用的轮胎。
