Cell surface markers are

Explanation

The correct answer is both b and d because both glycolipids and glycoproteins are classified as cell surface markers. Glycolipids are lipids with carbohydrate groups attached, found on the outer surface of cell membranes, playing critical roles in cell recognition and signaling. Glycoproteins, on the other hand, are proteins that have carbohydrates covalently bonded to them, and they also function in recognition and signaling processes at the cell surface. In contrast, lipoproteins primarily function in lipid transport in the bloodstream and are not cell surface markers. Sphingolipids, while important for membrane structure and signaling, are not specifically known as markers for cell recognition.