What is a primary function of the testes?

The primary function of the testes is the production of testosterone, which is a key male sex hormone. Testosterone plays a crucial role in the development of male reproductive tissues, as well as promoting secondary sexual characteristics such as increased muscle and bone mass, and the growth of body hair. Additionally, testosterone is essential for spermatogenesis, the process of sperm production, making it vital for male fertility.

While the other options might relate to different biological functions, such as oxygen exchange occurring in the lungs, filtration of blood performed by the kidneys, and absorption of nutrients being a function of the intestines, they do not pertain specifically to the primary role of the testes in the male reproductive system.