Final answer:
In the male reproductive system, there are two of each structure except for the prostate gland, of which there is only one. The correct answer to the given question is c. Prostate.
Step-by-step explanation:
The student's question pertains to the structures of the male reproductive system. In a normal male, there are two each of testes, seminal vesicles, ductus deferens, and ejaculatory ducts. However, there is only one prostate gland. Therefore, the correct choice among the options provided in the question is c. Prostate.
The testes are the site of sperm production and testosterone synthesis. Sperm are produced in the seminiferous tubules and matured and stored in the epididymides. The ductus deferens, also known as the vas deferens, carries sperm from the epididymides to the ejaculatory ducts, which in turn connect with the urethra. Seminal vesicles and the prostate gland add fluids to the sperm to create semen, while the bulbourethral glands also contribute to the seminal fluid.
In conclusion, the presence of a single prostate gland is the correct answer as it is the only structure listed that is not present in pairs in the male reproductive system.