(1969). Steps to spoken english: A graded course for spanish-speaking students. Longman.
Citazione stile Chigago Style (17a edizione)Steps to Spoken English: A Graded Course for Spanish-speaking Students. London: Longman, 1969.
Citatione MLA (9a ed.)Steps to Spoken English: A Graded Course for Spanish-speaking Students. Longman, 1969.
Attenzione: Queste citazioni potrebbero non essere precise al 100%.