Which of the following organs is part of the stallion's reproductive system?

The vas deferens is indeed a crucial component of a stallion's reproductive system, as it is responsible for transporting sperm from the epididymis to the urethra, where it can then be expelled during ejaculation. This structure plays an essential role in male fertility and reproduction.

In contrast, the ovary is part of the female reproductive system, where eggs are produced and hormones are secreted. The uterus, which is also part of the female reproductive system, is where a fertilized egg would implant and develop during pregnancy. Similarly, the fallopian tubes are another female reproductive structure that transports eggs from the ovaries to the uterus. Understanding these distinctions is important for comprehending the differences between male and female reproductive anatomy in horses.