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
2024-08-04
31
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:http://tihaiku.com/zcyy/3705173.html
相关试题推荐
Scientistsbelievetheyhavesolvedoneoftheenduringmysteriesofthesex
Scientistsbelievetheyhavesolvedoneoftheenduringmysteriesofthesex
Scientistsbelievetheyhavesolvedoneoftheenduringmysteriesofthesex
Scientistsbelievetheyhavesolvedoneoftheenduringmysteriesofthesex
Scientistsbelievetheyhavesolvedoneoftheenduringmysteriesofthesex
Scientistsbelievetheyhavesolvedoneoftheenduringmysteriesofthesex
Scientistsbelievetheyhavesolvedoneoftheenduringmysteriesofthesex
Scientistsbelievetheyhavesolvedoneoftheenduringmysteriesofthesex
Scientistsbelievetheyhavesolvedoneoftheenduringmysteriesofthesex
Scientistsbelievetheyhavesolvedoneoftheenduringmysteriesofthesex
随机试题
Heopenedthedoorandlethimselfinquietly______nottowakethefamily.A、be
【说明】假设你是公司的财务经理,写信向银行咨询业务。【内容】1.公司正在寻找一家服务好,收费合理的银行;2.公司目前有260名雇员、2800万
革兰阳性菌细胞壁的特殊组分为()A.几丁质 B.磷壁酸 C.胆固醇 D
不分布于脊柱区的浅血管是()A.椎动脉 B.肩胛背动脉 C.胸背动脉
C
超过()年未进行风险承受能力评估或发生可能影响自身风险承受能力情况的客户,再次
抵押是担保的一种方式,根据《物权法》的相关规定,下列说法正确的是()。
及时性要求企业对已经发生的交易或事项,应当及时进行确认、计量和报告,不得提前或延
下列关于劳动防护用品的说法中,错误的是()A.用人单位应当安排专项经费用于
施工图预算对建筑施工企业的作用包括()。A.建筑企业投标报价的基础 B
最新回复
(
0
)