(1987). Practice and reinforcement: (Purple level). New York: McDougal, Littell & Companay.
Trích dẫn kiểu ChicagoPractice and Reinforcement: (Purple Level). New York: McDougal, Littell & Companay, 1987.
MLA citiranjePractice and Reinforcement: (Purple Level). New York: McDougal, Littell & Companay, 1987.
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