Passage One
Finding fresh drinking water was not a problem in the Roman Empire. The ancient Romans built aqueducts (from the Latin words aqua, meaning "water," and ductus, meaning "channel"). The pipes and channels wound down hills and valleys, transporting freshwater from remote lakes and streams to cities. Engineers designed each aqueduct so that water would drop precisely 24 feet per mile. A steeper slope would bring too much water too quickly. Less of a slope would cause the water to stagnate. Stone bridges with multiple arches were built to support aqueducts where the land dipped too sharply. Many of the bridges can still be found in Europe. At the Roman Empire's peak in the first and second centuries, nearly 200 cities had water supplied by aqueducts.
Rome, the empire's capital, had 11 aqueducts for its estimated 1 million people. When the water reached Rome, it flowed into large containers, or tanks, on high ground. From there, it was distributed through pipes to different areas of the city. Some water was sold to rich citizens for their private use; some went to supply large public baths; the rest went to public fountains, located at crossroads throughout Rome that were never more than 109 yards apart. Experts say that each citizen of Rome could have used an average of 265 gallons of fresh, clean water per day — more than what's available in some cities today.
Stone bridges with multiple arches were built because__________.
A、 bridges made the cities more beautiful.
B、 bridges were necessary to connect cities.
C、 Europeans were fond of building bridges.
D、 some places were not high enough to support aqueducts.
【正确答案】：D
