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
2025-01-14
23
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/3911895.html
相关试题推荐
Itisnocoincidencethattherelationshipbetweenourcountrieshasaccompa
Insomecountrieswhereracialprejudiceisacute,violencehassocometob
Forcenturies,explorershaveriskedtheirlivesventuringintotheunknown
Emailcapturestheessenceoflifeatthecloseofthe20thcenturywithanauth
Emailcapturestheessenceoflifeatthecloseofthe20thcenturywithanauth
Emailcapturestheessenceoflifeatthecloseofthe20thcenturywithanauth
Emailcapturestheessenceoflifeatthecloseofthe20thcenturywithanauth
[originaltext]Iftheearthgetshotterinthenewcentury,whatwillhappen
[originaltext]Iftheearthgetshotterinthenewcentury,whatwillhappen
[originaltext]Iftheearthgetshotterinthenewcentury,whatwillhappen
随机试题
To:ParvatiMalikFrom:ChandrikaRaoDate:October2Subject:GPDSeminar
Evenifalmostnothingisknownabouttheneuroanatomyofsymboling,agreat
Whydoesthewritermention"athief"inthefirstparagraph?[br]Accordingto
Ironically,intheUnitedStates,acountryofimmigrants,prejudiceanddis
Sinceit’sourfirsttimetoworktogether,pleasesendinformationdescribingt
人们希望得到尊敬和社会的认可,这属于( )。A.生理需要 B.安全需要
下列各项中,不属于胎毒常见并发症的是A.丹毒 B.湿疹 C.胎黄 D.硬肿
具有"行气散结,降逆化痰"功效的方剂是()。A.枳实薤白桂枝汤B.半夏厚朴汤C
关于审慎性监督管理谈话制度作用的表述,正确的有()。A:使监管人员及时了解银行业
银行承兑汇票的承兑银行,应当按照票面金额向出票人收取()的手续费。A:千分之一
最新回复
(
0
)