Cobb, B. B., & Cobb, E. (1912). Busy builder's book: A problem book for individual work in the primary grades. Ginn.
Citace podle Chicago (17th ed.)Cobb, Bertha B., a Ernest Cobb. Busy Builder's Book: A Problem Book for Individual Work in the Primary Grades. Boston, New York: Ginn, 1912.
Citace podle MLA (8th ed.)Cobb, Bertha B., a Ernest Cobb. Busy Builder's Book: A Problem Book for Individual Work in the Primary Grades. Ginn, 1912.
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