What do M, J, M and B after the author mean in the references?

Description format of references \ x0d \ x0d \1periodical author. Title [j] Name of publication, year of publication, volume (issue): page number \x0d\\x0d\ 2 monograph author. Title [m]. Version (first edition not recorded). Place of publication:. 3 the author of prose collection. Title [c]. //editor. The name of the prose collection. Place of publication: publisher, year of publication. \x0d\\x0d\ Page number \ x0d \ 4 Dissertation author. Title [d] Storage location: storage unit, year \ x0d \. 6 standard number, standard name [s] \ x0d \ x0d \ 7 newspaper author. Title. Name of newspaper, publication date (edition) \ x0d \ x0d \ 8 Report author. Title [r]. Save location: year \ x0d \ x0d \