The correct answer is: D. phototropism.
Phototropism is a plant’s growth towards or away from a light source. It is a type of tropism, a growth movement that is caused by an external stimulus. The stimulus for phototropism is light, and the response is a bending of the plant towards the light source.
Geotropism is a plant’s growth in response to gravity. The stimulus for geotropism is gravity, and the response is a bending of the plant so that the roots grow down and the shoots grow up.
Thigmotropism is a plant’s growth in response to touch. The stimulus for thigmotropism is touch, and the response is a bending of the plant away from the source of touch.
Chemotropism is a plant’s growth in response to chemicals. The stimulus for chemotropism is a chemical, and the response is a bending of the plant towards the source of the chemical.
In conclusion, the correct answer is: D. phototropism.