更多"[不定项选择题]What is the main idea of th"的相关试题:
[不定项选择题]The best statement of the main idea of this passage is that__________.
A.scientists have found a way to prolong the period of clinical death
B.biological death occurs when vital organs have suffered permanent damage
C.modern scientists divide the process of dying into clinical and biological death
D.cooling delays the processes leading to biological death
[不定项选择题]共用题干
Rainmaking
1 The idea of rainmaking is almost as old as man,but it was not until 1946 that man succeeded in making rain.In ancient times,rainmakers had claimed to bring rain by many methods:dancing.singing-Kiiiing animals t including humans).
2 For a long time,men have understood where rain comes from.Water from the surface of oceans and lakes becomes part of the air,where it forms clouds from which rain falls.But exactly what starts the formation of raindrops was not known until quite recently.A man named John Aitken proved that drops of water gather around tiny bits of dust or other matter.The centers of the drops are so small that the human eye cannot see them.Without such centers,it seems raindrops do not form.
3 During World War Ⅱ,Dr.Irving Langmir,and his assistant Schaefer,were hired by the General Electric Company to study how and why ice forms on the wings of airplanes.They went to a mountain in New Hampshire,where snowstorms are common and cold winds blow.They were surprised to find that often the temperature of the clouds surrounding them was far below the freezing point,and yet ice did not form in the clouds.
4 After the War,Schaefer experimented with a machine that created cold,moist air similar to the air found in clouds.To imitate the moist air of a cloud,Schaefer would breathe into the machine.Then he would drop into the freezer a bit of powder,sugar,or some other substance.For weeks and months he tried everything he could imagine.Nothing happened.No crystals of ice were formed.None of the substances would serve as the center of a snow crystal or raindrops.
5 One July morning,Schaefer was dropping in bits of various substances and watching the unsuccessful results.Finally,a friend suggested that they go to eat lunch and Schaefer went with him.As usual,he left the cover of the freezer up,since cold air sinks and would not escape from the box.
6 Returning from lunch,Schaefer found that the temperature of the freezer had risen to a point higher than that required for ice crystals to remain solid.There were two choices now.He could close the cover and wait for the freezer itself to lower the air temperature,or he could make the process occur faster by adding dry ice-a gas in solid form that is very,very cold.He chose the latter plan.As he dropped the steaming white dry ice into the freezer,he happened to breathe out a large amount of air.And there,before his eyes,it happened!He had made ice crystals,not by adding centers to the moisture,but by cooling the breath so much that the liquid had to form crystals!Then he began to blow his breath into the freezer and drop large pieces of dry ice through it to create crystals which became a tiny snowstorm falling slowly to the floor of his laboratory.
7 After planning carefully,Schaefer made an experiment by dropping dry ice from his plane to the clouds below him.As was expected,snow formed and fell from the bottom of the cloud.Schaefer succeeded.He made history.
Man did not succeed in making rain until quite______.
A.imaginatively
B.recently
C.carefully
D.unscientifically
E.accidentally
F.satisfactorily
[不定项选择题]共用题干
Life Expectancy in the Last Hundred Years
A hundred years ago,life expectancy in developed countries was about 47:in the early 21st century,men in the United States and the United Kingdom can expect to live to about 74. Women to about 80, and these___1___ are rising all the time. What has brought___2___ these changes?When we look at the life___3___of people 100 years ago,we need to look at the greatest___4___of the time. In the early 20th century,these were the acute and often ___5___ infectious diseases such as smallpox. Many children died very young from these diseases and others,and the weak and elderly were always at risk. In the ___6 ___world these diseases are far___ 7 ___today,and in some cases have almost disappeared. A number of ___8 ___have led to this:improvements in sanitation and hygiene,the discovery and use of antibiotics,which ___9___ bacterial diseases much less dangerous,and vaccinations___10___ common diseases. ___11___ ,people's general health has improved with improvements in our general environ-ment:cleaner air,better means of preserving food,better and warmer housing,and better understanding of nutrition. Genetically,we should all be able to live to about 85 but ___12___ people do live longer today,there are still some big killers around that are preventing US from consistently reaching that age. The problems that affect people today are the more chro-nic illnesses,such as heart disease and strokes,and those ___13___ by viruses,such as influen- za and AIDS. Of course,cancer is a huge killer as well. In most cases these diseases affect ___14___ people,but there are worrying trends in the developed world with problems such as obesity ___15___ more heart disease and illnesses such as diabetes at younger ages.
The killers today can be classed as“lifestyle diseases”,which means that it may be possi- ble to halt their progress.
7._________
A.more deadly
B.deadly
C.less deadly
D.fatal
