In mammals, an important role of excretion is played by ________

Answer: Option B

The kidneys are bean-shaped organs that serve several excretory roles apart from the essential regulatory roles in mammals. They remove from the blood the nitrogenous wastes such as urea, as well as salts and excess water, and excrete them in the form of urine. In producing urine, the kidneys excrete nitrogenous wastes such as urea and ammonium.