The French port of Calais was closed on Saturday and that caused a huge backup of vehicles around the English port of Dover where ferry services were hit.

VOA: standard.2009.12.21

You really need that because if you have only one copy of something, you don't have a backup; so, you can store the one copy separately.

你真的很需要这项发明,因为要是你只有一份的话，你就没有备份;,这样的话，你就可以将副本单独留存。

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So it's like a backup.

所以，这就像是备用。

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