KREBS, R. D. (1971). Highway Materials. McGraw-Hill.
Lua i Stíl Chicago (17ú heag.)KREBS, Robert D. Highway Materials. McGraw-Hill, 1971.
Lua MLA (8ú heag.)KREBS, Robert D. Highway Materials. McGraw-Hill, 1971.
Rabhadh: Seans nach mbeach na luanna seo go hiomlán cruinn i ngach uile chás.