Which of the following structures is only a part of the male reproductive system in humans?

The male reproductive system is designed to make sperm or male gametes and is adapted to provide for the delivery of these gametes to the female to allow for fertilization. It consists of:1. Testes - produces sperm and the hormone testosterone2. Scrotum - pouch enclosing the testes keeping the sperm at an optimum temperature. 3. Vas deferens - tube that carries sperm away from the testes. 4. Prostate gland - adds lubricating and other fluids to the sperm. 5. Urethra - tube through the penis carrying sperm to the outside of the body. 6. Penis - adaptation for internal fertilization of the female.