【单选题】
The{{U}} (34) {{/U}}of a canal depends on the kind of boats going through it. The canal must be wide enough to permit two of the{{U}} (35) {{/U}}boats using it to{{U}} (36) {{/U}}each other easily. It must be deep enough to leave about two feet of water{{U}} (37) {{/U}}the keel of the largest boat using the canal. Some canals have sloping sides, while others have sides that are nearly{{U}} (38) {{/U}}.Canals that are cut through rock can have nearly vertical sides. {{U}} (39) {{/U}}, canals with earth banks may{{U}} (40) {{/U}}if the angle of their sides is too steep. Some canals are lined with brick, stone, or concrete to keep the water{{U}} (41) {{/U}}soaking into the muD、This also permits ships to go at{{U}} (42) {{/U}}speeds, since they cannot make the banks fall in by{{U}} (43) {{/U}}up the water. In small canals with mud banks, ships and barges (大平底船) must{{U}} (44) {{/U}}their speeD、
When the canal goes{{U}} (45) {{/U}}different levels of water, the ships must be{{U}} (46) {{/U}}or lowered from one level to the other. This is generally done by{{U}} (47) {{/U}}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{{U}} (48) {{/U}}it is the same as the upper level of water. Now the upper gates can be opened to{{U}} (49) {{/U}}the ship into the higher water. Sometimes a canal contains a series of locks when the{{U}} (50) {{/U}}in levels is very great.
B．Hence
C．Therefore
D．However
网考网参考答案：D
网考网解析：
[解析] 空前讲的是从岩石中开凿的运河两边的堤岸几乎是垂直的，空后讲的是土质堤岸的运河如果两边太陡峭就会导致坍塌，两句之间应是转折关系，故答案为[D]However。[A]Meanwhile“与此同时”；[B] Hence“因此”；[C]Therefore“因此”。 document.getElementById("warp").style.display="none"; document.getElementById("content").style.display="block"; 查看试题解析出处>>
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