The correct answer is option 1: Kidney. The kidney is responsible for excreting water, fat, and various catabolic wastes from the body. It is a vital organ of the urinary system that filters waste products, excess water, and other substances from the bloodstream to produce urine. The kidney also plays a role in maintaining the balance of fluids, electrolytes, and pH levels in the body.

Option 2: Skin is incorrect as although it does help in regulating body temperature by sweating, it primarily excretes water and electrolytes through sweat glands, not fat and catabolic waste.

Option 3: Spleen is incorrect as it is involved in the production and storage of blood cells, but it does not have a role in excreting water, fat, or catabolic waste.

Option 4: Salivary glands are responsible for producing saliva, which aids in digestion, but they are not involved in excreting water, fat, or catabolic waste.

Alert - correct answer should be option 1: Kidney.