What is the primary structural difference between sphingolipids and glycerolipids?

Sphingolipids are more abundant in eukaryotic cell membranes than glycerolipids.

Sphingolipids contain ester linkages, while glycerolipids contain amide linkages.

Sphingolipids have more variable fatty acids than glycerolipids.

Sphingolipids use a sphingosine molecule as the platform, while glycerolipids use a glycerol molecule.