Answer: The two starting materials for a Robinson annulation are a ketone (or aldehyde) and a conjugated diene.
Explanation: In the Robinson annulation reaction, a ketone or aldehyde undergoes a Michael addition with a conjugated diene, followed by an intramolecular aldol condensation. This process leads to the formation of a cyclic compound, typically a six-membered ring. The ketone or aldehyde serves as the electrophile, while the conjugated diene acts as the nucleophile.