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
Someday, in【C1】______ the outer planets of our solar system, humankind will want to do【C2】______ send small probes that merely
Someday, in【C1】______ the outer planets of our solar system, humankind will want to do【C2】______ send small probes that merely
admin
2013-06-02
31
问题
Someday, in【C1】______ the outer planets of our solar system, humankind will want to do【C2】______ send small probes that merely fly rapidly by them. In time, we will want【C3】______ spacecraft that will go【C4】______ orbit around these alien planets, land robots on their moons, and even return rock and soil sample back to Earth.【C5】______ , we will want to send humans to their moons, on at least【C6】______ which liquid water—the fundamental requirementfor life【C7】______ we know it—is believed to be【C8】______ .
For missions such as these, we will need rockets powered by a nuclear reaction【C9】______ igniting chemicals. Chemical rockets have served us well. But the【C10】______ low amount of energy that they can deliver for a given mass of fuel is a severe【C11】______ when dispatching spacecraft【C12】______ long distances. To reach the outer planets, for example, a chemically-powered space vehicle must【C13】______ fuel by having a very small mass and making【C14】______ use of gravity "assists", in which the craft maneuvers close enough to a planet for the planet’s gravity to propel the craft forward,【C15】______ its speed.
In technical term, chemical rockets have low【C16】______ velocity growth, which means that their exhaust velocities are not high enough to【C17】______ very high speed to the rocket. Nuclear rockets,【C18】______ their chemical counterparts, could impart a maximum velocity of【C19】______ about 22 kilometers a second. Such a high velocity would make possible a direct path to Saturn (土星), reducing travel time from about seven years to as【C20】______ as three.
【C18】
选项
A、in contrast to
B、in addition
C、with regard to
D、contrary to
答案
A
解析
逻辑衔接题。本处意思是为:与化学燃料火箭相比,核能火箭…。故选A in contrast to“与…对比”。
转载请注明原文地址:https://kaotiyun.com/show/E2n7777K
0
大学英语六级
相关试题推荐
Itisnotthe"somedayIwillwinthelottery"kindofdaydream,butthekindthattapsintothehidden,partofyourbrain.Tha
Itisnotthe"somedayIwillwinthelottery"kindofdaydream,butthekindthattapsintothehidden,partofyourbrain.Tha
A、ItwaseasytoshipfromEngland.B、Horsesoccasionallyateitiftherewasnograinavailable.C、Peopletookitwiththemwhe
A、Johnwasdisappointedathismathscore.B、Johndidbetterthanhethoughthewasableto.C、Johndidn’tpass,althoughhehad
ArtificialIntelligenceI’msurethatHansMoravecisatleastassaneasIam,buthecertainlybroughttomindtheclassic
Inviewofthepracticalneedofsociety,_____________________________(有越来越多的人对学习英语感兴趣).
Scotlandisauniqueplace.IthassomeofthemostbeautifulcitiesinEurope,alivingevidenceofasplendidandproudpast.
Scotlandisauniqueplace.IthassomeofthemostbeautifulcitiesinEurope,alivingevidenceofasplendidandproudpast.
Scotlandisauniqueplace.IthassomeofthemostbeautifulcitiesinEurope,alivingevidenceofasplendidandproudpast.
随机试题
含硫油品的沉积物为什么会自燃?
心理学通常以人们掌握概念的途径不同将概念分成日常概念和
患者空腹血糖11.1mmol/L(200mg/dl),尿糖阳性,多食、多饮、多尿。患者尿量增多的原因是
下列不属于X线管电参数的是
下列不属于基金客户服务的原则的是()。
根据公司法律制度的规定,下列选项中,属于上市公司监事会职权有()。(2002年)
全陪导游员要根据旅游团的不同类型和实际需要准备相关知识,了解和充实客源国(地)的()等方面的知识。
项目范围说明书说明了为什么要进行这个项目,明确了项目目标和主要可交付成果,是项目实施的重要基础。项目和子项目都要编写范围说明书。一般来说,项目范围说明书要由项目团队来写。项目范围说明书是项目团队和项目委托方双方签订协议的基础,项目利益相关者通过项目范围说明
[*]
有如下程序代码:PrivateSubForm_Click()DimxAsInteger,yAsInteger,BumAsIntegerX=3y=xDoUntilx>=6num
最新回复
(
0
)