D. Thigmotropism. A "tropism" is a plant movement in response to an environmental stimulus, and "tropo" means "touch." Plant cells change their movements when they detect a change in pressure after having contacted something. It is not A because germination is the sprouting of seedlings. It is not B because photosynthesis is the action of plants to convert light energy into chemical energy. It is not C because phototropism refers to movement in response to a change in light ("photo" means "light").
