备而不用
- na.have sth. ready just in case
- 网络Keep thing seven years and you will find a use for it; have sth ready just in case; have something ready just in case

备而不用
1.have sth. ready just in case; be better to get ready for nothing than caught unprepared; have a thing but not to use it for the time being; Keep a thing seven years and you will find a use for it.; keep sth. for possible future use; put aside for possible use in the future
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