Under what conditions is a sphingolipid classified as a ceramide?

• A. When the variable head group is a glycosidic linkage.
• B. When the variable head group is absent, forming an ester linkage.
• C. When the variable head group is a hydrogen atom, forming an amide linkage.
• D. When the variable head group is a phosphate group, forming an ester linkage.

Answer: (C)