Cell recognition via carbohydrate chains Steps:

• Identify role of cell surface molecules: recognition depends on specific markers for immune response, signaling, and adhesion.
• Examine choices: focus on components with carbohydrate moieties that serve as antigens or receptors.
• Eliminate structural lipids/proteins without recognition roles.
• Select pair that both contribute to cell identity and interaction.

Why D is correct:

• Glycoproteins and glycolipids contain oligosaccharide chains that act as recognition sites, enabling cell-cell identification per fluid mosaic model.

Why the others are wrong:

• A: Cholesterol stabilizes membrane fluidity; glycoproteins aid recognition, but cholesterol does not.
• B: Phospholipids form the bilayer but lack specific recognition functions.
• C: Glycolipids contribute, but excludes glycoproteins, which are equally vital for recognition.

Final answer: D