(D) Auxins — Auxin diffuses towards the shady side of the shoot, stimulating cells to grow longer on the side away from light, causing the shoot to bend towards light.
The passage directly states: "This concentration of auxin stimulates the cells to grow longer on the side of the shoot which is away from light." Adrenaline is an animal hormone (not a plant hormone), while cytokinins promote cell division and gibberellins promote stem growth — neither causes phototropic bending. Auxin is the correct answer.