The correct answer is option 3, Phytochrome. Phytochrome is a plant pigment that helps plants sense and respond to changes in light quality, particularly in the red and far-red regions of the light spectrum. It acts as a photoreceptor, absorbing red light and converting it into a biologically active form. It also has the ability to absorb and respond to far-red light. This pigment plays a crucial role in regulating various plant processes such as seed germination, stem elongation, and flowering. Carotenoids (option 1) are another group of plant pigments, but they mainly absorb in the blue and green regions of light. Chlorophyll (option 2) absorbs strongly in the blue and red regions of light, but not specifically in the far-red region. Cryptochrome (option 4) is a pigment involved in regulating light-dependent processes but does not specifically absorb in the red and far-red regions.