Obee, B. (1998). Cambridge first certificate: Grammar and usage. Cambridge University Press.
Cita Chicago (17th ed.)Obee, Bob. Cambridge First Certificate: Grammar and Usage. Cambridge: Cambridge University Press, 1998.
Cita MLA (8th ed.)Obee, Bob. Cambridge First Certificate: Grammar and Usage. Cambridge University Press, 1998.
Atenció: Aquestes cites poden no estar 100% correctes.