例句：
You should make a copy of the disk as a backup.
你应该将磁盘复制一个备份。
The police had backup from the army.
警方得到了军方的增援。
Every part of the system has a backup.
这套系统的每个部分都有备件。
Sharon also sang backup for Barry Manilow.
莎伦还为巴里·马尼洛唱了伴唱。
We can use him as a backup if one of the other players drops out.
如果有参赛者退出，我们可以用他作为替补。