Answer: B. all systems work together to maintain homeostasis
The human body is designed in such a way that all the cells, tissues, organs, and systems work together to achieve a level of balance, and ensure that the body is in the right condition. In other words, all the systems of the body work together to maintain homeostasis (the ability of the body to maintain a state of internal balance, while adapting to the conditions outside the body).
Almost all the processes involved in human metabolism are controlled by hormones, so option A is out of it.
Each system is interconnected in unique ways, and each system relies on other systems for seamless functions. This also goes to show that each system is unable to work on its own, as all the systems are directly connected. This disqualifies options C and D.