APA

I. C. S. Reference library a series of textbooks prepared for the students of the international correspondence school and containing in permanent form the instruction papers, examination questions, and keys used in their various courses : conversational lessons. s.l. : Scranton International Textbook company, s.a: .

Chicago

I. C. S. Reference library a series of textbooks prepared for the students of the international correspondence school and containing in permanent form the instruction papers, examination questions, and keys used in their various courses : conversational lessons. s.l. : Scranton International Textbook company, s.a: .

Harvard

I. C. S. Reference library a series of textbooks prepared for the students of the international correspondence school and containing in permanent form the instruction papers, examination questions, and keys used in their various courses : conversational lessons. s.l. : Scranton International Textbook company, s.a: .

MLA

s.l. : Scranton International Textbook company, s.a: . .