TOEFL Listening: ETS-TOEFL听力机经 - RJ454X179OGOF6T6P$

According to the professor, what might have contributed to the popularity of the human-transport hypothesis? A. New physical evidence of transport devices used in the Bronze Age has been found. B. The hypothesis has become familiar over time. C. Until recently no other hypothesis had been suggested. D. The scientists who support the hypothesis are well respected.