Answer:
The correct answer will be option 3.
Step-by-step explanation:
A stimulus is a change in the chemical and physical structure of an organism external and internal environment which can be easily detected.
The organism can respond to the stimulus by showing physiological as well as morphological changes. This is known as sensitivity which can be observed easily in the sunflower. The sunflowers respond to the abiotic factors like sunlight by bending in the direction of the sunlight. The sunflower moves with the direction of light that is from east to west. This is a complex physiological process which is known as the "heliotropism".
Thus, option 3 is the correct answer.