Brown Gfrorer, B. S. S. (1977). Basic english for students of Natural and applied sciences / Brown Gfroner, Bonnie; García Charpentier, Miriam; González Murillo, Trinidad; Trejos Montero, Elisa; Umaña Aguiar, Jeanina. Universidad de Costa Rica.
Chicago-čujuhus (17. p.)Brown Gfrorer, Bonnie; Smith Sharp. Basic English for Students of Natural and Applied Sciences / Brown Gfroner, Bonnie; García Charpentier, Miriam; González Murillo, Trinidad; Trejos Montero, Elisa; Umaña Aguiar, Jeanina. San José, Costa Rica: Universidad de Costa Rica, 1977.
MLA-čujuhus (9. p.)Brown Gfrorer, Bonnie; Smith Sharp. Basic English for Students of Natural and Applied Sciences / Brown Gfroner, Bonnie; García Charpentier, Miriam; González Murillo, Trinidad; Trejos Montero, Elisa; Umaña Aguiar, Jeanina. Universidad de Costa Rica, 1977.