APA

Betz F., . (1948). Learning German: a first book. New York: American Book Co.

Chicago

Betz Frederick, . 1948. Learning German: a first book. New York: American Book Co.

Harvard

Betz F., . (1948). Learning German: a first book. New York: American Book Co.

MLA

Betz Frederick, . Learning German: a first book. New York: American Book Co. 1948.