Final answer:
The endocrine system helps maintain homeostasis by secreting hormones that regulate various body functions necessary for a stable internal environment. It works in conjunction with the nervous system to make ongoing adjustments that keep physiological variables within a set range.
Step-by-step explanation:
The system that aids in maintaining homeostasis by constant adjustments is the nervous system and the endocrine system. However, specifically filling in the blank for the provided question with an appropriate choice from A to D, the correct answer is B. Endocrine system.
The endocrine system secretes hormones that are crucial in regulating various body functions such as metabolic rate, blood sugar levels, and temperature, all of which are part of the homeostatic processes. Although the nervous system also plays a key role in homeostasis by providing rapid responses and fine control, the question specifically asks which system, given the options, helps maintain a steady state, and therefore the endocrine system is the focus.