TOEFL Listening: ETS-TOEFL听力机经 - 83QS1I91G4SM4W7MP$

What point does the professor make about blue and ultraviolet wavelengths? A. They are the only wavelengths of light that fruit flies can perceive. B. They must be present in order for cryptochrome in fruit flies to be activated. C. Studies show that fruit flies cannot distinguish them. D. Fruit flies rely on them exclusively for detecting the location of food.