Which of the following plant growth regulators promotes internode elongation prior to flowering in cabbage ?

Gibberellins promote internode elongation just prior to flowering in rosette plants like cabbage, beet, and many other plants with a rosette habit. This phenomenon is known as bolting.

Ethephon is a source of ethylene, which promotes fruit ripening and abscission.

Abscisic acid acts as a general plant growth inhibitor and stress hormone.

Indole butyric acid is a synthetic auxin widely used to induce rooting in stem cuttings.

Answer: Gibberellin