What is the primary role of testosterone in the male body?

Testosterone plays a crucial role in the maturation of sperm, which is essential for male fertility. It is produced primarily in the testes and is vital for the development and maintenance of male reproductive tissues, including the testes and prostate, as well as secondary sexual characteristics such as increased muscle and bone mass. The hormone stimulates the production of sperm in the seminiferous tubules of the testes, meaning that without adequate levels of testosterone, sperm maturation cannot occur effectively. This role is fundamental to male reproductive health, making it the primary function of testosterone in the male body. The other choices do not pertain to the main functions of testosterone. For instance, regulating blood sugar levels primarily involves insulin, while increasing calcium absorption is mainly the function of vitamin D, and promoting muscle relaxation does not directly relate to the role of testosterone.