Gray, E., & O'Sullivan, N. Practice Tests for the PET 1 Preliminary English Test: Class CDs. Express Publishing.
Chicago-viite (17. p.)Gray, Elisabeth, ja Neil O'Sullivan. Practice Tests for the PET 1 Preliminary English Test: Class CDs. Newbury: Express Publishing.
MLA-viite (8. p.)Gray, Elisabeth, ja Neil O'Sullivan. Practice Tests for the PET 1 Preliminary English Test: Class CDs. Express Publishing.
Varoitus: Nämä viitteet eivät aina ole täysin luotettavia.