Which of the following best describes a Robinson annulation?

A reaction involving intramolecular self-condensation of a 1,5-dicarbonyl compound to form a six-membered enone.

A reaction involving the formation of a five-membered lactone from an ester and an alcohol.

A reaction involving the oxidation of an aldehyde to form a carboxylic acid.

A reaction involving the addition of hydrogen to an alkene to form a saturated compound.