Soars, J. &. L. Headway. Student's book. Pre-intermediate. (9a ed.). Oxford University Press.
Chicago Style (17th ed.) CitationSoars, John & Liz. Headway. Student's Book. Pre-intermediate. 9a ed. New York, Estados Unidos: Oxford University Press.
MLA (9th ed.) CitationSoars, John & Liz. Headway. Student's Book. Pre-intermediate. 9a ed. Oxford University Press.