TOEFL Listening: TPO-TOEFL阅读TPO - I5IR2A94G125TR55N$

According to paragraph 2, what was true of the waterpower mills built throughout the Roman Empire? A. Most had horizontal-axis wheels B. Their design was based on mills that had long been used in Scandinavia C. Their design was more popular beyond the Empire's boundaries than it was within the Empire. D. They are more advanced than the mills used in the Middle East at an earlier time.