Which of the following is NOT one of the nine organ systems in the human body?

The correct answer is "Thermal" because it does not represent an organ system within the human body. Instead, the human body consists of nine recognized organ systems that work together to maintain overall health and functionality. These include the digestive, respiratory, and reproductive systems, which are vital for processes such as breaking down food, exchanging gases, and facilitating reproduction, respectively.

Thermal regulation is indeed an important function for maintaining body temperature, but it is not classified as a separate organ system like the others listed. Rather, temperature regulation is managed through mechanisms involving various systems, such as the integumentary (skin), nervous, and circulatory systems, rather than functioning as a standalone system.