Homeostasis regulates the body's internal environment Steps:

• Identify the question: seeks the mechanism maintaining stable internal conditions in humans.
• Recall key biological concept: the body uses dynamic equilibrium to control variables like temperature, pH, and ion levels.
• Match to options: evaluate which term describes overall regulation within narrow limits.
• Eliminate mismatches: focus on broad control, not specific processes.

Why A is correct:

• Homeostasis is the process that maintains a stable internal environment by regulating physiological variables within narrow limits, as defined by Walter Cannon.

Why the others are wrong:

• B: Excretion removes wastes but is a specific function, not the overarching control mechanism.
• C: Positive feedback amplifies deviations (e.g., blood clotting), destabilizing rather than stabilizing conditions.
• D: Respiration exchanges gases for energy but does not broadly control all internal aspects.

Final answer: A. homeostasis