首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
For centuries men dreamed of achieving vertical flight. In 400 AD Chinese children played with a fanlike toy that spun upwards a
For centuries men dreamed of achieving vertical flight. In 400 AD Chinese children played with a fanlike toy that spun upwards a
admin
2010-05-26
32
问题
For centuries men dreamed of achieving vertical flight. In 400 AD Chinese children played with a fanlike toy that spun upwards and fell back to earth as rotation ceased. Leonardo da Vinci conceived the first mechanical apparatus, called a "Helix", which could carry a man straight up, but this was only a design and was never tested.
The ancient dream was finally realized in 1940 when a Russian engineer piloted a strange-looking craft of steel tubing with a rotating fan on top. It rose awkwardly and vertically into the air from a standing start, hovered a few feet above the ground, went sideways and backwards, and then settled back to earth. That vehicle was called a helicopter.
Imaginations were fired. Men dreamed of going to work in their own personal helicopters. People anticipated that vertical flight transports would carry millions of passengers as do the airlines of today. Such fantastic expectations were not fulfilled. The helicopter has now become an extremely useful machine. It excels in military missions, carrying troops, guns and strategic instruments where other aircraft cannot go. Corporations use them as airborne offices, many metropolitan areas use them in police work, construction and logging companies employ them in various advantageous ways, engineers use them for site selection and surveying, and oil companies use them as the best way to make offshore and remote work stations accessible to crews and supplies. Any urgent mission to a hard to-get-to place is a likely task for a helicopter. Among their other multitude of uses: deliver people across town, fly to and from airports, assist in rescue work, and aid in the search for missing or wanted persons.
Under what conditions are helicopters found to be absolutely essential?
选项
答案
Helicopters are essential for any urgent mission.
解析
从最后一段倒数两句话可看出,在很多紧急情况下而人类又很难到达的地方,直升机的使用是必需的。
转载请注明原文地址:https://jikaoti.com/ti/AZLFFFFM
0
大学英语四级
相关试题推荐
A、Theydon’thelpsportsplayersatall.B、Theydon’tliveuptotheirfame.C、Theymaybecomfortablebutaxetooexpensive.D、
A、Theythoughtitwastheweaponofthegods.B、Theythoughtitwaselectricity.C、Theythoughtitwasfireworkofthegods.D、T
______(如果他下午来),Ishouldaskhimtohelpus.
A、Jessieshouldknowthemarketingdirectorbetter.B、Jessieiswrongtofindfaultwithherboss.C、Jessieseemstohavealot
A、Doingcredittoone’scommunity.B、Distinguishingoneself.C、Gettingrichquickly.D、Respectingindividualrights.B
Asresearcherslearnmoreabouthowchildren’sintelligencedevelops,theyareincreasinglysurprisedbythepowerofparents.T
FromthetopofTempleIV,densejunglecanopy(遮篷)spreadstothehorizonineverydirection.Some215feetbelowliesTikal,th
FromthetopofTempleIV,densejunglecanopy(遮篷)spreadstothehorizonineverydirection.Some215feetbelowliesTikal,th
MedicareinAmericaWhenDrugPricesAreoutofReachTrueStory.ElderlyanduninsuredAmericanspaythehighestpric
A、Doctorandnurse.B、Customerandwaitress.C、Bossandsecretary.D、Managerandclerk.B
随机试题
当前,国际投资格局深刻调整,我国利用外资工作面临新形势、新特点、新挑战。为进一步做好利用外资工作,稳定外资规模,优化外资结构,国务院印发《关于进一步做好利用外资工作的意见》。关于该文件的内容,下列说法正确的是()。①允许外国保险集团公司投资设立保
早期牙龈炎的临床症状是
关于古代司法诉讼制度的表述,说法不正确的是:
背景资料:某闸室基础开挖是闸室分部工程中的一部分,其中右岸边墩(长8m×宽1.8m,开挖底高程为23.0m)基础开挖单元工程中的软基开挖工序质量评定表部分内容如下表所示。该工程项目单元工程质量评定表由监理单位填写,土坝单位工程
背景资料某会议中心新建会议楼工程,为保证室内外装饰效果,经研究决定,装修工程采取单独招标,独立开发,采用公开招标的形式确定施工队伍,建设单位与施工单位按照《建设工程施工合同(示范文本)》签订了装饰装修施工合同。招标阶段,在招标文件中明确了如下部分条款:(
在PowerPoint中放映当前幻灯片的快捷键为()。
倾斜移动
安全电子交易协议SET是由VISA和MasterCard两大信用卡组织联合开发的电子商务安全协议。以下关于SET的叙述中,正确的是(59)________________。
下列选项中可以查看Python代码的语言版本(例如3.5.3)的是
Researchershavefoundthatpeople’smentalabilitiespeakat22beforebeginningtodeterioratejustfiveyearslater.Theresu
最新回复
(
0
)