References cannot come directly from Zhihu, but must be related books and documents. In the file, it can't be related to Baidu on the Internet. The requirement of the paper is high, so the formal paper cannot directly quote Zhihu's content.

According to GB3469-83 "File Types and File Carrier Codes", reference file types and file types are identified by a single letter:

Monograph m; Newspaper n; Journal j; Patent document p; Compilation g; Ancient books o; Technical standards;

Dissertation d; Scientific and technological report; Reference tool k; Search tool w; File b; Tape a;

Chart q; Record l; Product sample x; Video tape v; Meeting minutes; Chinese translation test;

Music score I; Movie y; Manuscript h; Microfilm u; Slide z; Miniature flat film f; Other e.