APA

Black C. E., Helmreich E. C., . (1952). Twentieth century Europe: a history. New York: Knopf.

Chicago

Black Cyril Edwin, Helmreich Ernst Christian, . 1952. Twentieth century Europe: a history. New York: Knopf.

Harvard

Black C. E., Helmreich E. C., . (1952). Twentieth century Europe: a history. New York: Knopf.

MLA

Black Cyril Edwin, Helmreich Ernst Christian, . Twentieth century Europe: a history. New York: Knopf. 1952.