APA

Heinlein R. A., . (1989). Tunnel in the sky. New York: Del Rey.

Chicago

Heinlein Robert A, . 1989. Tunnel in the sky. New York: Del Rey.

Harvard

Heinlein R. A., . (1989). Tunnel in the sky. New York: Del Rey.

MLA

Heinlein Robert A, . Tunnel in the sky. New York: Del Rey. 1989.