Debate as to whether or not fish are color-blind ended years ago. Research has established that the rods and the cones found in the eyes of certain fish enable them to distinguish colors. Fish with bony skeletons, such as trout and bass, have both rods and cones in their eyes. They see their watery world in living color. The eyes of other fish, sharks and skates, for example, have rods but no cones. They are color-blind. Science, however, has not yet discovered if fish prefer certain colors over others.

Q. Underline the sentence which indicates that the matter of fish and color preference is still being studied.