首页
登录
职称英语
Someday, in【C1】______ the outer planets of our solar system, humankind wil
Someday, in【C1】______ the outer planets of our solar system, humankind wil
游客
2024-05-05
30
管理
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. [br] 【C9】
选项
A、other than
B、regardless of
C、instead of
D、rather than
答案
D
解析
短语辨义题。本处意思是:我们需要以核反应能量为动力的火箭,而不是燃烧化学品的火箭。故选D rather than“而不是”。
转载请注明原文地址:https://tihaiku.com/zcyy/3585590.html
相关试题推荐
Ourcurrenteducationalsystemhasnotbeenableto__________(跟上当今世界经济和科技发展步伐)
Americanculturehasbeenenrichedbythevaluesandbeliefsystemsofvirtu
Americanculturehasbeenenrichedbythevaluesandbeliefsystemsofvirtu
Americanculturehasbeenenrichedbythevaluesandbeliefsystemsofvirtu
Americanculturehasbeenenrichedbythevaluesandbeliefsystemsofvirtu
Americanculturehasbeenenrichedbythevaluesandbeliefsystemsofvirtu
Americanculturehasbeenenrichedbythevaluesandbeliefsystemsofvirtu
Americanculturehasbeenenrichedbythevaluesandbeliefsystemsofvirtu
Americanculturehasbeenenrichedbythevaluesandbeliefsystemsofvirtu
Americanculturehasbeenenrichedbythevaluesandbeliefsystemsofvirtu
随机试题
"I’mnot100%convincedthatmemorizingthedictionaryisthebestwayofim
HowtoPresentaSeminarPaperUniversitystudentsof
ApprenticeshipshavelongbeenpopularinEurope,butworkforce-orientedhig
Thefactthatthemanagementistryingtoreachanagreement______fiveseparate
Thereisprobablynolimittowhatsciencecandointhewayofincreasingp
Youshouldspendabout20minutesonQuestions28-40whicharebasedonReading
AccordingtoascientificstudypublishedinApril,2015,birdshaveshownt
施工现场必须设置“五牌一图”,其中“一图”指的是( )。A、组织机构图 B、
S模式规定,国有资产控股企业经营者期股的获取方式主要包括()。A.经营者用现金
共用题干 某部件加工的时候,设计尺寸10mm(误差为+0.010,-0.005
最新回复
(
0
)