神仙鱼左倾45
extra 超过必要的数量的备份reserve 比较正式的用法，多用于积存意义的备用，比如粮食的库存，积蓄，存款等方面a reserve stock (备用品)spare多余的，备用的，有事先准备好进行备用的意思back up 备份等等 有的是含有事先准备好的意思。其实有好多词都有比较雷同的意思，需要看具体的语境来选择一个更加适合的词。 以上
0度空间的鱼
Backup; spare; reserve; standby; alternate 请问是备用什么呢？ e.g., Most hospitals have backup generators in case of blackouts. It's best to always carry a spare tyre when driving long distances. I had to dip into my reserve funds when the business got into trouble.
