Below is a text with blanks. Click on each blank, a list of choices will appear. Select the appropriate answer choice for each blank.
下面的文本有一些空格。点击每个空格会出现一组选项，请为每个空格选出最合适的答案。
Clean water was very important to the Romans. Cities, towns and forts were built near springs. However, as Roman cities and towns grew, they needed to bring in water from . As the population grew, did the need for clean water. Trying to shift large of water underground in pipes was not possible as lead pipes would be too weak and bronze pipes would be too expensive. The Romans could not make cast iron pipes as the for doing this were not known to them. If water could not be brought via pipes, the Romans decided to bring it overland in what were conduits. When the water got to the city, it was fed off into smaller bronze or ceramic pipes. To get the water to flow at an even (and slow) pace, conduits were built on a slight slope. Valleys were crossed by using aqueducts. One of the most famous of these is the Pont du Gard aqueduct at Nimes in southern France. Where possible, the Romans did take water through tunnels but the hills needed to be relatively small for this to be successful.
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