Gray, E., & O'Sullivan, N. (2003). Practice Tests for the PET 1 Preliminary English Test: Teacher's Book. Express Publishing.
Citazione stile Chigago Style (17a edizione)Gray, Elisabeth, e Neil O'Sullivan. Practice Tests for the PET 1 Preliminary English Test: Teacher's Book. Newbury: Express Publishing, 2003.
Citatione MLA (8a ed.)Gray, Elisabeth, e Neil O'Sullivan. Practice Tests for the PET 1 Preliminary English Test: Teacher's Book. Express Publishing, 2003.
Attenzione: Queste citazioni potrebbero non essere precise al 100%.