首页
登录
职称英语
Over the centuries, scientists have been trying hard to find satisfactory su
Over the centuries, scientists have been trying hard to find satisfactory su
游客
2023-10-11
34
管理
问题
Over the centuries, scientists have been trying hard to find satisfactory substitutes for precious stones but failed many times.
Many years ago, a chemist surprised the world by saying: It should be possible to make a precious stone that not only looks like the real thing, but that is the real thing.The only difference should be that one crystal would be made by man, the other by nature.
At first this did not seem like a particularly hard task.
Scientists began to try making synthetic diamonds towards the end of the eighteenth century and discovered a key scientific fact
: diamonds are a form of carbon, which is a very common element.
Then, why not change a cheap and plentiful substance, carbon, into a rare and expensive one, diamond?This change takes place in nature, so it should be possible to make it happen in the laboratory.
It should be possible, but for 150 years every effort failed though several people believed that they had solved the diamond riddle during this period.
The real success came after the scientists realized that, in changing carbon into diamonds, unbelievably heavy pressure and extremely high temperature are indispensable, and carbon needs to be dissolved(溶解) in a metal that helps the reaction to take place more easily.
Under these conditions, a number of shiny crystals were produced in the laboratories of the General Electric Company.The results of careful analysis showed that the chemist was right: these jewels of the laboratory were not like diamonds; they were diamonds. [br] If something is indispensable (Paragraph 6), it is _____.
选项
A、enormously helpful
B、relatively useless
C、absolutely necessary
D、reasonably valuable
答案
C
解析
转载请注明原文地址:https://tihaiku.com/zcyy/3090555.html
相关试题推荐
Feedbackmatters.Whetherwearetryingtofindourwaytoanewfriend’sh
Feedbackmatters.Whetherwearetryingtofindourwaytoanewfriend’sh
Feedbackmatters.Whetherwearetryingtofindourwaytoanewfriend’sh
Feedbackmatters.Whetherwearetryingtofindourwaytoanewfriend’sh
Feedbackmatters.Whetherwearetryingtofindourwaytoanewfriend’sh
Feedbackmatters.Whetherwearetryingtofindourwaytoanewfriend’sh
Feedbackmatters.Whetherwearetryingtofindourwaytoanewfriend’sh
Chocolatecouldsoonbeathingofthepast,afterscientistswarnedthatthe
Chocolatecouldsoonbeathingofthepast,afterscientistswarnedthatthe
Chocolatecouldsoonbeathingofthepast,afterscientistswarnedthatthe
随机试题
[originaltext]M:Mom,couldyougivemeafewdollarssoIcouldseeamoviewi
UncleTom’sCabinandRootsaretwonovels,whichgiveavividdescriptionofth
Unlessmeasuresaretakenatonce,thereisapossibilitythatalltheocean
根据我国《反不正当竞争法》,构成商业秘密的技术信息和经营信息必须具备的条件包括(
资料 某市审计局于2016年4月派出审计组,对国有控股的临江钢铁有限公司20
某社区为提高辖区内老年糖尿病患者的管理水平,引进某健康管理机构为糖尿病患者进行服
灌砂法测定密度时,下部可以略小于上部,以有利于灌砂。()
培训课程修订的程序包括:①确定修订流程的频率;②公布修订流程;③确定修订流程的范
将总资金M的一部分投资于一个股票组合,这个股票组合的β值为βs,占用资资金S,剩
《烟花爆竹安全管理条例》规定,申请举办焰火晚会以及其他大型焰火燃放活动,主办单位
最新回复
(
0
)