Today, most countries in the world have canals. Some canals, such as the Suez or the Panama, 【B1】ships weeks of time by making their voyage a thousand miles shorter. Other canals permit boats to reach cities that are not located on the coast【B2】other canals drain lands where there is too much water, help or【B3】fields where there is not enough water.
The【B4】of a canal depends art the kind of boats going through it. The canal must. be wide enough to permit two of the【B5】boats using it to【B6】each other easily. It must be deep enough to leave about two feet of water【B7】the keel of the largest boat using the canal.
Some canals have sloping sides, while others have sides that are nearly【B8】. Canals that are cut through rock can have nearly vertical sides【B9】, canals with earth banks may【B10】if the angle of their sides is too steep. Some canals are lined with brick, stone, or concrete to keep the water【B11】soaking into the mud. This also permits ships to go at【B12】speeds, since they cannot make the banks fall in by【B13】up the water. In small canals with mud banks, ships and barges(大平底船) must【B14】their speed.
When the canal goes【B15】different levels of water, the ships must be【B16】or lowered from one level to the other. This is generally done by【B17】of locks. If a ship wants to go up to higher water, the lower end of the lock opens to let the boat in. Then this gate closes, and the water is let into the lock chamber from the upper level. This raised the level of the water in the lock【B18】it is the same as the upper level of water. Now the upper gates can be opened to【B19】the ship into the higher water. Sometimes a canal contains a series of locks when the【B20】in levels is very great.
【B1】

A. take
B. save
C. cost
D. waste