Concept:
Exocrine glands are classified based on secretion mechanism.
• Merocrine
• Apocrine
• Holocrine
Step 1: Understand sebaceous glands.
Sebaceous glands release sebum by complete disintegration of cells.
This mode is called:
\[
\boxed{\text{Holocrine secretion}}
\]
Hence sebaceous glands are holocrine glands.
Therefore option (D) is correct.