Gray, E., & O'Sullivan, N. (2003). Practice Tests for the PET 1 Preliminary English Test: Student's Book. Express Publishing.
Chicago-viite (17. p.)Gray, Elisabeth, ja Neil O'Sullivan. Practice Tests for the PET 1 Preliminary English Test: Student's Book. Newbury: Express Publishing, 2003.
MLA-viite (8. p.)Gray, Elisabeth, ja Neil O'Sullivan. Practice Tests for the PET 1 Preliminary English Test: Student's Book. Express Publishing, 2003.
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