What is the primary function of the kidneys in the human body?

The primary function of the kidneys is to filter waste from the blood. The kidneys are vital organs that help maintain homeostasis by removing waste products and excess substances from the bloodstream, which are then excreted as urine. In doing so, the kidneys also help regulate electrolyte balance, blood pressure, and fluid balance in the body. This filtration process is essential for preventing the buildup of harmful substances in the blood and for maintaining the body's overall health.

In addition to waste removal, the kidneys also play roles in regulating pH levels and producing certain hormones, but their main and most crucial function is the filtration of blood to produce urine, making option B the correct answer.