Steroids are crystallizable lipids having four hydrocarbon rings consisting of three cyclohexane and one cyclopentane ring and a long hydrocarbon side chain. Fatty acids are absent. In animals, sterols are precursors of steroid hormones and vitamin D. Cholesterol is a sterol of animal systems which form bile salts, is a component of plasma membrane and hormone. LDL (low-density lipoprotein) helps to reduce the cholesterol which is part of plasma membrane i.e., sterol of animal system. Thus, the correct answer is A.