Read the following paragraph and answer the question. Give ONLY the answer, no other words or explanation.

For example:

Answer: <most likely answer, as short as possible>.

Paragraph: 
Male Reproductive Structures. Organs of the male reproductive system include the penis, testes, and epididymis. Several ducts and glands are also part of the system. Do you know the reproductive functions of any of these structures?.


Question: Organs of what male biological system include the penis, testes, and epididymis?
reproductive system
Male reproductive system.