[填空题]When required in tonnage quantities, oxygen is prepared by the’ fractional distillation of liquid air. The process takes advantage of the fact that when a ______ gas is allowed to expand, it cools. (compress)

[填空题]When required in tonnage quantities, oxygen is prepared by the’ fractional distillation of liquid air. The process takes advantage of the fact that when a ______ gas is allowed to expand, it cools. (compress)

[填空题]oxygen

[单项选择]{{B}}Interview Two{{/B}}

When Vet was pregnant, her mother and sisters were everything she needed them to be but ______.

[单项选择]When did President Obama first contact Haitian President Rene Preval, after the quake
A. On Thursday
B. On Friday
C. On Saturday

[简答题]Chemical Oxygen Demand

[简答题]Fires need oxygen(氧气). Without oxygen they will die. Cover a fire with water, sand, or sometimes with your coat. (Passage 3 )

[填空题]To separate hydrogen from oxygen needs electricity that can be created by______.

[单项选择]Scientists believe that there is not enough oxygen in the Moon’s atmosphere to（　）plant life.
A. adapt
B. personalize
C. sustain
D. describe

[单项选择]Differences in positions adopted by oxygen and hydrogen atoms account for variations in the crystalline structure of different forms of ice.（　）
A. are caused by
B. explain
C. derive from
D. constitute

[单项选择]We know that oxygen is necessary for the breathing of animals and plants and for burning. Only one-fifth of air holds oxygen, but this is quite enough for all ordinary uses. Pure oxygen is used for special kinds of breathing and burning, for instance, patients in hospital and research workers working in high mountainous district.
High up about the earth air is not so plentiful. On the top of a mountain our lungs would not take in as much oxygen at each breath as they would at the bottom, and on very high mountains, breathing is so difficult that men have little strength.
Air has enough oxygen for the burning of a fire. Pure oxygen would cause the wood or coal to burn so fast that it would be wasted. When a very hot fire is needed for a special purpose, oxygen is supplied instead of air.
______ cannot live without oxygen.
A. Plants
B. Animals
C. Human beings
D. A, B and C

[填空题]Houdini managed to get oxygen from air pockets caught between ______.

[填空题]Humans are dependent on oxygen and water for (survive)（）