which of the following is a lipid?

* Lactose is a disaccharide sugar that is found most notably in milk and is formed from galactose and glucose.

* Cholesterol is an organic chemical substance classified as a waxy steroid of fat. It is an essential structural component of mammalian cell membranes and is required to establish proper membrane permeability and fluidity.

* Collagen is a group of naturally occurring proteins found in animals, especially in the flesh and connective tissues of mammals.

* Nicotine is an alkaloid found in the nightshade family of plants (Solanaceae); biosynthesis takes place in the roots and accumulation occurs in the leaves.

* Aniline, phenylamine or aminobenzene is an organic compound with the formula C6H5NH2. Consisting of a phenyl group attached to an amino group, aniline is the prototypical aromatic amine.

Answer: Cholesterol. Cholesterol is a chemical compound that is naturally produced by the body and is structurally a combination of lipid (fat) and steroid. Cholesterol is a building block for cell membranes and for hormones like estrogen and testosterone. About 80% of the body's cholesterol is produced by the liver, while the rest comes from our diet. The main sources of dietary cholesterol are meat, poultry, fish, and dairy products. Organ meats, such as liver, are especially high in cholesterol content, while foods of plant origin contain no cholesterol. After a meal, dietary cholesterol is absorbed from the intestine and stored in the liver. The liver is able to regulate cholesterol levels in the blood stream and can secrete cholesterol if it is needed by the body.

Cholesterol is the answer you're looking for.

Cholesterol (LDL, HDL, VLDL, triglycerides)