- A Gibberellin
- B Ethylene
- C Auxin
- D Cytokinin
Correct answer: B. Ethylene
Explanation: The triple response (inhibition of elongation, radial swelling, and horizontal growth of seedlings) is a well-known bioassay used to detect ethylene activity.
Concept context
Phases of plant growth, the five classical plant hormones plus newer ones, photoperiodism, vernalization, and seed dormancy.