Twaddell, W. F. (1963). The english verb auxiliaries (2a ed.). Brown University Press.
Cita Chicago Style (17a ed.)Twaddell, W. F. The English Verb Auxiliaries. 2a ed. Rhode Island: Brown University Press, 1963.
Cita MLA (9a ed.)Twaddell, W. F. The English Verb Auxiliaries. 2a ed. Brown University Press, 1963.
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