Step 1: Male reproductive system overview. The primary functions involve male gamete (sperm) production and hormone generation, such as testosterone. Spermatogenesis, the process of sperm creation, takes place within the testes.
Step 2: Spermatogenesis process. Sperm production occurs in the seminiferous tubules of the testes. These tubules contain germ cells and Sertoli cells, which support sperm development.
Step 3: Analysis of alternative choices.
Prostate gland: Generates seminal fluid, providing nourishment and protection to sperm.
Seminal vesicles: Contribute to the formation of seminal fluid.
Epididymis: Facilitates sperm storage and maturation; it does not produce sperm.
Therefore, the accurate answer is (D) Testes.