The difference between a liquid and a gas is obvious under the conditions of temperature and pressure commonly found at the surface of the Earth. A liquid can be kept in an open container and fill it to the level of a free surface. A gas forms no free surface but tends to diffuse throughout the 11 available; it must therefore be kept in a closed container or held by a gravitational field, as in the 12 of a planet s atmosphere. The distinction was a 13 feature of early theories describing the phases of matter. In the nineteenth century, for example, one theory maintained that a liquid could be dissolved in a vapor without losing its identity, and another theory 14 that the two phases are made up of different kinds of molecules. The theories now prevailing take a quite different approach by emphasizing what liquids and gases have in 15 They are both forms of matter that have no 16 structure, and they both flow readily.
The fundamental similarity of liquids and gases becomes clearly apparent when the temperature and pressure are 17 somewhat. Suppose a closed container 18 filled with a liquid is heated. The liquid expands, or in other words becomes less dense; some of it evaporates. In contrast, the vapor above the liquid surface becomes denser as the evaporated molecules are 19 to it. The combination of temperature and pressure at which the densities become 20 is called the critical point.
A. added
B. case
C.prominent
D.held
E. equal
F. partially
G.example
H.previous
I. space
J, lifted
K.permanent
L.particularly
M. extended
N. raised
0.common
上一篇: 大学四级考试词汇必备练习精析(3)
下一篇: 大学英语四级考试常考短语短句的精讲(7)
国际英语资讯:Spotlight: U.S. experts warn tariffs would diminish investment, hamper productivity growth
体坛英语资讯:Poland to invest in football innovation
国内英语资讯:Chinas 2nd Import Expo attracts over 250 Fortune 500 companies, industry leaders
Love From My Mother 妈妈的爱
国际英语资讯:18 injured after Bangladeshi plane skids off runway at Myanmars airport
体坛英语资讯:Bayern roll 5-1 over Frankfurt to clinch their 7th successive Bundesliga title
国际英语资讯:President Kiir vows to stabilize South Sudan
国内英语资讯:Armenian PM to attend Asia civilization dialogue conference in China
国内英语资讯:Taiwan question brooks no foreign interference: spokesperson
国内英语资讯:China firmly opposes any foreign interference in Hong Kongs affairs: FM spokesperson
国际英语资讯:U.S. House panel votes to hold attorney general in contempt of Congress
国际英语资讯:Japanese, Russian defense ministers express respective concerns over military issues
The Real Culture 真正的文化
我的朋友黛西
地球未来很“凄惨”?100万个物种正遭受灭绝威胁
国际英语资讯:Putin says Russia to continue boosting defense potential
体坛英语资讯:China win 2 golds on day 1 of FINA diving World Series in London
国内英语资讯:Wife of Chinese president meets international students
一株垂垂老矣的常青藤
体坛英语资讯:Monaco win relegation battle, PSG welcome trophy with four-goal rout
体坛英语资讯:Indonesian sport climbing world champion to defend title in Chinas Wujiang
大学老师怎么看待慢学生?
体坛英语资讯:Ajax beat Tottenham 1-0 in first leg of Champions League semifinal
国际英语资讯:Prince Harry and Meghans baby boy named Archie
国内英语资讯:Commentary: U.S. move on Taiwan question puts China-U.S. ties in jeopardy
2019年6月大学英语四级作文范文:工作和家庭哪个更重要
国内英语资讯:Foreign businesses remain optimistic of investment in China: FM
国内英语资讯:Vice premier stresses quality nursing services
国际英语资讯:Palestinian FM condemns Israeli settlements
国内英语资讯:Efforts needed to make military ties stabilizer for China-U.S. relationship: spokesperson