Final answer:
Danazol is the androgen drug most commonly used to treat endometriosis, due to its ability to create a high-androgen and low-estrogen environment, leading to the atrophy of endometrial tissue.
Step-by-step explanation:
The androgen drug most commonly used to treat endometriosis is b) Danazol. Danazol is a synthetic hormone that suppresses the production of gonadotropins and subsequently decreases estrogen levels, leading to atrophy of endometrial tissue. By creating a high-androgen and low-estrogen environment, it mimics menopause and relieves symptoms associated with endometriosis.