I think the answer would be Vitamin D because the rest of the choices are characteristics of hair (cholesterol is what makes hair look/ appear oily; UV radiation is what hair protects your scalp from; and keratin [particularly dead keratin] is what your hair is made of) .... Whereas with vitamin D is what the skin produces and doesn't have any involvement with hair.
Hemoglobin
Durable.
HDL cholesterol is the good cholesterol because is flows in the bloodstream and removes harmful cholesterol from the areas in which it doesn't belong. If you have high HDL levels of cholesterol it will reduce your chance of getting heart disease.
Lipid is a term that is used to describe all types of fats. Cholesterol's structure falls under the category of lipids.
what's cholesterol's function as in the cell membrane
Cholesterol is a member of the alcohol group, as proven by its distinctive -ol suffix. It is thus an organic compound.
Keratin does not belong because the reticular layer, dermal papillae, and Meissner's corpuscles are all structures found in the dermis of the skin, whereas keratin is a fibrous protein that is mainly found in the outermost layer of the skin, the epidermis.
conduction
Keratin fibrils do not belong as they are a specific component of intermediate filaments found in epithelial cells, while keratohyaline and lamellated granules are associated with keratinization in the epidermis.
Cholesterol belongs to the group of organic compounds known as sterols. Sterols are a subgroup of steroids that contain a hydroxyl group at the C-3 position of the A-ring.
Teeth do not belong because they are not made of the same protein (keratin) as skin, hair, and nails.
Cholesterol molecules are considered to be lipids since they are a class of steroids which are lipids. Cholesterol is hydrophobic due to its hydrocarbon composition; this is a commonality within lipids.