The correct option is D Unsaturated fatty acid
Smooth E.R. of animal cell does not synthesize unsaturated fatty acid. The smooth endoplasmic reticulum has functions in several metabolic processes. It synthesizes lipids, phospholipids, and steroids. Cells which secrete these products, such as those in the testes, ovaries, and skin oil glands have a great amount of smooth endoplasmic reticulum. It also carries out the metabolism of carbohydrates, drug detoxification, attachment of receptors on cell membrane proteins, and steroid metabolism.