Which of the following best describes the function of the kidneys?

The function of the kidneys is primarily to filter waste products from the blood and regulate various aspects of bodily functions, including blood pressure. The kidneys filter out toxins and excess substances from the bloodstream, which are then excreted as urine. This filtration process is crucial for maintaining homeostasis, as it helps regulate the balance of electrolytes, fluids, and waste in the body, thereby affecting blood volume and pressure.

In addition to filtering blood, the kidneys produce hormones that are vital for blood pressure regulation, such as renin, and they also play a role in red blood cell production by releasing erythropoietin. Therefore, the comprehensive role of the kidneys encompasses both waste removal and essential regulatory functions, making option B the most accurate description of their function.

The other options do not accurately reflect kidney function; for instance, insulin production occurs in the pancreas, respiration involves the lungs, and digestion is primarily the role of the gastrointestinal tract.