TOEFL Listening: ETS-TOEFL听力机经 - G4KSV8R3I09QELJ8P$

Why does the professor mention the size of ancient Rome's population? A. To suggest that Rome's citizens could have used more water than they did B. To compare the number of inhabitants to that of modern cities C. To explain why many Romans built houses outside the city D. To explain why Rome needed to import water from outside the city