The subject of a document is used to express the main purpose of the document and summarize the characteristics of the document. Therefore, its meaning must be clear and clear, and the concept used must be accurate. We must first consider whether the chosen subject is ambiguous, whether Summarize the main purpose of the document; secondly, consider whether the chosen keywords are in compliance with the "Thesaurus of the State Council Official Document Thesaurus", and the insufficient attention to the keywords must be corrected. What is the main point of support in the above statement? ['How to review subject terms.', 'How to modify the keywords.', 'How to write keywords.', 'Importance of keywords.']