Homeostasis is primarily achieved through the maintenance of internal stability within the body, which involves various physiological processes that regulate temperature, pH, hydration, and other vital conditions. The most relevant option in your list that addresses how homeostasis is achieved is:
Cells maintain internal stability.
While the other options (secreting enzymes, controlling involuntary and voluntary movements) can contribute to specific bodily functions, maintaining internal stability encompasses a wider range of physiological mechanisms that work together to keep the body's internal environment consistent despite external changes.