n.后援；備份；備用

Liu Bei was given 1,000 troops as the back up force. 劉備帶一千人馬作后援。

You can back up and restore full-text catalogs. 可以備份和還原全文目錄。

This option will back up files on the volume. 該選項將備份卷中的文件。

You should carry a spare wheel in the back of your car. 你應(yīng)在車后帶一個備用的輪胎。