求翻译：关于关键词

　　求翻译：关于关键词。这句话翻译：
Immediately after the abstract, provide a maximum of four keywords. Each keyword should be
accompanied by the capital letter denoting the category from which the keyword has been selected.
Click here for a complete list of keywords (PDF version)

问题：每个关键词前面都要带大写字母？

问题2：这些字母有什么可以查询？
===有问必答===
不是这个意思，是关键词必须从该提供的列面选择。
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那如果有一些关键词在它所给的题库里没有怎么办呢？