总是备份你下载的任何音乐，以防电脑崩溃。

Always ___back ___up any music you download in case your computer crashes.

你应该定期备份你的重要文件。

You should ___back ___up your important files regularly.

在删除之前别忘了备份它。

Don't forget to ___back it ___up before you delete it.