NIEBEL, B. W. Methods, standars and work design#Benjamin W. Niebel, Andris Freivalds. McGraw-Hill.
Lua i Stíl Chicago (17ú heag.)NIEBEL, Benjamin W. Methods, Standars and Work Design#Benjamin W. Niebel, Andris Freivalds. McGraw-Hill.
Lua MLA (8ú heag.)NIEBEL, Benjamin W. Methods, Standars and Work Design#Benjamin W. Niebel, Andris Freivalds. McGraw-Hill.
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