Answer:
B: Phytochrome
Step-by-step explanation:
Photoperiodism refers to the induction of flowering in plants in response to photoperiods. Phytochromes are the blue green pigments that sense the light and dark periods. Phytochorome exists in two interchangeable forms that are regulated by ratio of red to far-red light. Exposure of Pr form of phytochrome to red light converts it into Pfr form which is physiologically active form and restore the flowering process.