APA

Gruber R., . (1960). Puerto Rico: island of promise. New York: Hill and Wang.

Chicago

Gruber Ruth, . 1960. Puerto Rico: island of promise. New York: Hill and Wang.

Harvard

Gruber R., . (1960). Puerto Rico: island of promise. New York: Hill and Wang.

MLA

Gruber Ruth, . Puerto Rico: island of promise. New York: Hill and Wang. 1960.