首页
登录
职称英语
Today, most countries in the world have canals. Even in the twentieth centur
Today, most countries in the world have canals. Even in the twentieth centur
游客
2023-12-23
25
管理
问题
Today, most countries in the world have canals. Even in the twentieth century, goods can be moved more cheaply by boat than by 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 not located on the coast, Still other canals drain lands where there is too much water, help to irrigate fields where there is not enough water, and furnish water power for factories and mills.
The size of a canal depends on the kind of boats going through it. The canal must be wide enough to permit two of the largest boats using it to pass each other easily. It must be deep enough to leave about two feet of water beneath the keel of the largest boat using the canal.
Some canals have sloping sides, while others have sides that are nearly vertical. Canals that are cut through rock can have nearly vertical sides. However, canals with earth banks may crumble if the angle of their sides is too steep.
Some canals are lined with brick, stone, or concrete to keep the water from soaking into the mud. This also permits ships to go at greater speeds, since they cannot make the banks fall in by stirring up the water. In small canals with mud banks, ships and barges must limit their speed.
In places where it does not rain very often, irrigation canals drain water from rivers or lakes and carry it to fields. Sometimes artificial lakes, such as the lake behind the Aswan Dam on the Nile river, 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 covering the land, as it did in the past.
Many countries have built canals near the coast, and parallel to the coast. These waterways make it possible for boats to travel between ports along the coast without being exposed to the dangers of the open sea. [br] Canals in soft, muddy land have sides which are______.
选项
A、straight
B、sloping
C、vertical
D、steep
答案
B
解析
转载请注明原文地址:https://tihaiku.com/zcyy/3297335.html
相关试题推荐
DuringJapan’srevolutioninthe19thcentury,theJapanesedenouncedtheirown
[originaltext]Themostimportanttrendsinearly20thcenturyarchitecturesimp
[originaltext]Themostimportanttrendsinearly20thcenturyarchitecturesimp
[originaltext]Themostimportanttrendsinearly20thcenturyarchitecturesimp
[originaltext]WelcometoEastTimor,oneoftheworld’snewestcountries,a
[originaltext]WelcometoEastTimor,oneoftheworld’snewestcountries,a
Whichofthefollowingistrue?[br][originaltext]Lotsofcountries,lotsofb
Whichofthefollowingistrue?[originaltext]Lotsofcountries,lotsofbusines
HowwastheBritisharchitecturestylecharacterizedintheearly20thcentury?
HowwastheBritisharchitecturestylecharacterizedintheearly20thcentury?
随机试题
Theperiodduring(when)people(learnedto)smeltironis(called)(the)IronA
Ofallthesoldierstheyhadthe______ofbeingthemostfearless,themostpatr
电控燃油喷射系统由燃油供给系统和电子控制系统两部分组成。()
加气混凝土砌块长度规格为600mm,常用的高度规格尺寸有三种,下列哪种不是其常用
患者,男,25岁,在车库修车时不慎引燃汽油,导致头面部及双手烧伤,入院检查时发现
为了实现项目目标,项目人力资源管理的目的是()。A、调动与项目相关的所有人员
面对因新冠疫情导致“缩水”的春季学期,各地各校_______,有的重新安排时间表
下列不是经营机构禁止进行销售服务的是( )。A.向投资者就不确定事项提供确定性的
甲将电脑出租给乙,租期半年。乙在使用电脑期间,被丙偷走,丙将该电脑出卖给不知情的
咖啡因在苯甲酸钠的存在下溶解度由1:50增至1:1是由于A.增溶 B.防腐
最新回复
(
0
)