TOEFL Listening: ETS-TOEFL听力机经 - M23T8HA0N3TQ7713P$

How did biologists research the function of cryptochrome? A. By breeding fruit flies without the gene that produce cryptochrome B. By studying its genetic makeup. C. By training fruit flies to fly toward a magnet. D. By comparing the photo receptors of fruit flies with those of other insects.