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
39
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] The passage suggests that a canal with earth sides may be lined with concrete, so that______.
选项
A、the boats can go faster
B、the water will be cleaner
C、the water will flow faster
D、the canal will be less dangerous
答案
A
解析
转载请注明原文地址:https://tihaiku.com/zcyy/3297336.html
相关试题推荐
Inmanycountriestobaccoandmedicinearegovernment________.A、controlB、monop
Fornearlyacentury,twoUnitedStatesgovernmentalagencies,theUnitedSt
Fornearlyacentury,twoUnitedStatesgovernmentalagencies,theUnitedSt
Fornearlyacentury,twoUnitedStatesgovernmentalagencies,theUnitedSt
Fornearlyacentury,twoUnitedStatesgovernmentalagencies,theUnitedSt
Fornearlyacentury,twoUnitedStatesgovernmentalagencies,theUnitedSt
Wefindthatsomebirdstraveltwiceayearbetweenhotandcoldcountries.A、tra
Thegulfbetweenthetwocountriescannotbebridged,andtheiropinionsareso
DuringJapan’srevolutioninthe19thcentury,theJapanesedenouncedtheirown
Representativesofthegovernmentsof47countries,22internationalorganiza
随机试题
Itisnotoftenrealizedthatwomen【C1】______ahighplaceinsouthernEurope
Impressionismisaformofartthatbeganinthe1870’s.Whenyoulookclose
切身利益vitalinterest
已知:某企业上年营业收入为6900万元,总资产平均余额为2760万元,流动资产平
既能行气止痛,又能温肾散寒药为()。A.川楝子B.乌药C.荔枝核D.木香E.沉
关于浸提的叙述不正确的是A:浸提过程包括浸润、渗透、解析、溶解、扩散等阶段B:
根据规定,银行工作人员为客户服务时要做风险提示,下列做法不正确的是()。A:提醒
A.止痛 B.涩肠 C.固脱 D.止带 E.燥湿诃子除敛肺外还能(
劳动过程中的管理中,属于防护设备设施和个人防护用品的主要管理工作内容的有()。
大体积混凝土应优先考虑水泥性质中的()。A.强度 B.变形 C.水化热
最新回复
(
0
)