Gaya APA

Leffingwell, B. (1977). English Usage Drills and Exercises Progammed for the Typewriter . New York: Mc Graw-Hill book company.

Gaya MLA

Leffingwell, Brendel. "English Usage Drills and Exercises Progammed for the Typewriter". New York: Mc Graw-Hill book company, 1977. .