【正确答案】 C

【答案解析】[解析]
Today, most countries in the world have canals. Goods can be moved cheaply by boat than any other means of transport. Some canals, such as the Suez or the Panama, save ships weeks of time by making their voyage a thousand miles shorter. Other canals permit boats to reach cities that are located on the coast. Still other canals help to irrigate fields where there is not enough water, and drain lands where there is too much water.
In places where it does not rain very often, irrigation canals carry water from rivers or lakes, such as the lake behind .the Aswan Dam on the Nile River, and provide the irrigation water.
In places where there is too much water, canals can drain the water off the land for use in farming. In Holland, acres and acres of land have been drained in this way. Since much of this drained land is below sea level, the water in the canals has to be pumped up to sea level. Dikes have been built in Holland to keep the sea from coveting the land.