Gray, E., & O'Sullivan, N. Practice Tests for the PET 1 Preliminary English Test: Class CDs. Express Publishing.
Cita Chicago Style (17a ed.)Gray, Elisabeth, y Neil O'Sullivan. Practice Tests for the PET 1 Preliminary English Test: Class CDs. Newbury: Express Publishing.
Cita MLA (8a ed.)Gray, Elisabeth, y Neil O'Sullivan. Practice Tests for the PET 1 Preliminary English Test: Class CDs. Express Publishing.
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