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
As in the field of space travel, so in undersea exploration new technologies continue to appear. They share a number of similari
As in the field of space travel, so in undersea exploration new technologies continue to appear. They share a number of similari
admin
2012-09-19
74
问题
As in the field of space travel, so in undersea exploration new technologies continue to appear. They share a number of similarities with each other—as well as some important differences.
Manned submersibles.(潜水器), like spaceships, must maintain living conditions in an unnatural environment. But while a spaceship must simply be sealed against the vacuum of space, a submersible must be able to bear extreme pressure if it is not to break up in deep water.
In exploring space, unmanned vehicles were employed before astronauts. In undersea exploration, on the other haled, men paved (铺路) the way, and only recently have unmanned remote-operated vehicles (ROVs) been put to use.
One reason for this is that communicating with vehicles in orbit is much easier than talking to those underwater. A vacuum is an ideal medium for radio communications, but underwater communications are limited to much slower sound waves. Thus, most undersea vehicles—particularly ROVs—operate. at the end of long process.
For a similar reason, knowing where you are undersea is much more difficult than in space. A spaceship’s position can be located by following its radio signal, or by using telescopes and radar. For an undersea vehicle, however, a special network of sonar (声纳) devices most be laid out in advance on the ocean floor in the area of a dive to locate the vehicle’s position.
Though undersea exploration is more challenging than outer space in a number of respects, it has a distinct advantage: Going to the ocean doesn’t require the power necessary to escape Earth’s gravity. Thus, it remains far less expensive.
Ocean exploration is not so expensive as space travel mainly because ______.
选项
A、most undersea vehicles operate at tile end of long ropes
B、ROVs have been put to use
C、it is not affected by Earth’s gravity
D、there is no need for submersibles to get away from Earth’s gravity
答案
D
解析
第六段最后两句:潜入洋底不需要脱离地球引力所需的动力,这样花费就少得多
转载请注明原文地址:https://kaotiyun.com/show/Cr57777K
0
大学英语四级
相关试题推荐
A、Becausetheyareinahurry.B、Becausetheyarestrange.C、BecausetheycannotwatchTV.D、Becausetheyhaveotherschedules.
Geographyisthestudyoftherelationshipbetweenpeopleandtheland.Geographers(地理学家)compareandcontrast【C1】______places
Geographyisthestudyoftherelationshipbetweenpeopleandtheland.Geographers(地理学家)compareandcontrast【C1】______places
A、ThenucleartransferB、TheprocesstakingDNAC、ThenormalreproductiveprocessD、ThecreationofcellsC克隆是个热门话题,有关克隆的文章无非谈论
Inpolicework,youcanneverpredictthenextcrimeorproblem.Noworkingdayisidenticaltoanyother,sothereisno"【B1】__
Jan.6issue--Theweatheroutsidewasicy,butinside,250journalistsweregatheredinaManhattanofficecomplextoseethela
Thesubjectisnotincludedinthe______,soImustgiveyousomeadditionallessons.
A、Theywentcampingthistimelastyear.B、Theydidn’tquiteenjoytheirlastpicnic.C、Theylearnedtocooperateunderharshco
Adviceto"sleeponit"couldbewellfounded,scientistssay.Afteragoodnight’ssleep,aproblemthatseemedinsurmountable
随机试题
一般职务作品的著作权归()。
某公司由于拓展业务的需要,资金供应链紧张,经公司管理层决议,计划向社会发行企业债券。该公司财务经理已经编制好筹资计划,请代该公司设计债券发行批准制度。
以各项护理活动为中心的护理工作方法称为()
A.水B.电解质C.纤维蛋白原D.白蛋白E.红细胞
甲将抢得的信用卡交给何某,并告何某系抢劫所得,唆使何某去ATM机取钱,何某取现4万元,二人各分得2万元。对此,下列选项错误的是()。
独立的理财顾问不可以是()。
下列各项中,不属于营业成本的是()。
A公司和B公司有关债务重组资料如下:A公司销售给B公司一批商品,含税价款为1237.5万元,债务到期时款项尚未收到,由于B公司发生财务困难,2014年1月1日双方进行债务重组。经修改债务条件,A公司同意将债务本金减到900万元,同时将剩余债务延期一年,并按
近年来,个人信息泄露事件_______,公民个人的信息安全面临越来越严峻的挑战。除了相关领域的立法,政府在执行层面都有待加强之外,一个很重要的原因就是民众对于信息保护的观念还非常_______。之前就有人在自己的微博上公开明星信息,丝毫没有意识到自己违反了
下图(a)所示为一个模块层次结构的例子,图(b)所示为对其进行集成测试的顺序,则此测试采用了(1)测试策略。该测试策略的优点不包括(2)。(1)
最新回复
(
0
)