Bywater, F. (1990). A Proficiency Course in English with Key (1se ed., 18th reprinting.). Nelson.
Cita Chicago Style (17a ed.)Bywater, F.V. A Proficiency Course in English with Key. 1se ed., 18th reprinting. Walton-on-Thames: Nelson, 1990.
Cita MLA (9a ed.)Bywater, F.V. A Proficiency Course in English with Key. 1se ed., 18th reprinting. Nelson, 1990.
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