You are shown three structural diagrams: Diagram X shows a glycerol backbone esterified to three long hydrocarbon chains; Diagram Y shows a glycerol backbone with two hydrocarbon chains and a phosphate-containing head; Diagram Z shows a four-ring fused structure. Match X, Y, Z to triglyceride, phospholipid, and sterol respectively and explain a key distinguishing chemical feature for each.

• A. X = triglyceride (glycerol + three fatty acids); Y = phospholipid (glycerol + two fatty acids + phosphate head); Z = sterol (multi-ring fused structure such as cholesterol).
• B. X = sterol because three hydrocarbon chains always indicate a four-ring nucleus; Y = triglyceride because the phosphate group indicates esterification to three fatty acids; Z = phospholipid due to ringed aromaticity.
• C. X = phospholipid because all phospholipids have three tails; Y = sterol because phosphate groups are found in cholesterol; Z = triglyceride because rings are common in glycerol backbones.
• D. X = carbohydrate polymer because three hydrocarbons imply sugar linkages; Y = peptide lipid hybrid due to phosphate-associated amino groups; Z = synthetic polymer unrelated to biological lipids.

Answer: (A)