Brown Gfrorer, B. S. S. Listen, speak, read and understand. Universidad de Costa Rica.
Chicago Style (17. basım) AtıfBrown Gfrorer, Bonnie; Smith Sharp. Listen, Speak, Read and Understand. San José, Costa Rica: Universidad de Costa Rica.
MLA (9th ed.) AtıfBrown Gfrorer, Bonnie; Smith Sharp. Listen, Speak, Read and Understand. Universidad de Costa Rica.
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