Answer:
The correct answer is option - b.
Explanation:
Auxin is one of the plant hormones that consist of characteristics like morphogen. It has a cardinal role in plant body growth and development by a process that regulates behavioral and growth in the life cycle of a plant.
In this experiment, he must have added too much of auxin to the experimental plant as auxins are toxic to the plants if present in large concentrations. If too much auxin added to the plant body it stimulates the production of ethylene which causes fall of leaves and stops the elongation growth.
Thus, the correct answer is option B.