Answer:
D. a signal; a chemical; auxin
Step-by-step explanation:
Phototropism is described as a phenomenon that involves the growth of a specific organism as an outcome towards a light stimulus. It is generally observed or found in plants yet occurs in a few other organisms, for example, fungi. The different cells that are being found on the plants that are placed far from the light posses a specific chemical known as 'auxin' that generally reacts when the "phototropism" occurs.