The excretory functions of the urinary system are performed by the

Kidneys

Explanation:

One of the primary functions of the urinary system is the excretion of metabolic wastes. Urea is the primary nitrogenous end product of metabolism in human beings. Other excretory waste products in humans are ammonium, creatinine, and uric acid. Kidneys excrete metabolic waste by urine formation. Urea, ammonia, creatinine, uric acid, and urobilin contain nitrogen and therefore, are collectively known as nitrogenous wastes. Other wastes excreted in the urine are foreign substances that have entered the body, drugs and environmental toxins.

Kidneys produce urine in three steps: glomerular filtration, tubular reabsorption, and tubular secretion. Water accounts for almost 95% of the volume of urine and the remaining 5% consist of electrolytes, nitrogenous end products and substances derived from drugs.

the answer will be a) proteins i believe