There is a smell of gas in the hold. You must wear your （）(氧气面罩).A、fire maskB、breathing apparatusC、life-jacketD、fire drill

共用题干
Natural Gas

1 Natural gas is produced from reservoirs deep beneath the earth's surface. It is a fossil fuel（矿物燃
料）,meaning that it is derived from organic material buried in the earth millions of years ago.The main corn-
ponent of natural gas is methane（甲烷）.
2 The popularity and use of clean natural gas have increased dramatically over the past 50 years as
pipeline infrastructure（基础设施）has been installed to deliver it conveniently and economically to millions
of residential,commercial and industrial customers worldwide.Today,natural gas service is available in all 50
states in the U.S.,and is the leading energy choice for fueling American homes and industries.More than 65
million American homes use natural gas.In fact,natural gas is the most economical source for home energy
needs,costing one-third as much as electricity. In addition to heating homes,much of the gas used in the United
States is used as a raw material to manufacture a wide variety of products,from paint,to fibers for clothing,to
plastics for healthcare,computing and furnishings.Natural gas is also used in a significant number of new
electricity-generating power plants.
3 Natural gas is one of the safest and cleanest fuels available. It emits（发出）less pollution than other
fossil fuels sources. When natural gas is burned,it produces mostly carbon dioxide（二氧化碳）and water va-
por一the same substances emitted when humans breathe.Compared with some other fossil fuels,natural gas
emits the least amount of carbon dioxide into the air when combusted（燃烧）一making natural gas the clea--
nest burning fossil fuel of all.
4 The United States consumes about one-third of the world's natural gas output,making it the largest
gas-consuming region in the world.The U.S.Department of Energy Information Administration forecasts that
natural gas demand will grow by more than 50 percent by 2025.
5 There are huge reserves of natural gas beneath the earth's surface.The largest reserves of natural
gas can be found in Russia , West and North Africa and the Middle East. LNG（液化天然气）has been pro-
duced domestically and imported in the United States for more than four decades.Today,the leading import-
ers of LNG are Japan,Korea,France and Spain.

Paragraph 4 ______________
A:Popularity and Use of Natural Gas
B:Natural Gas Reserves and Supply
C:Natural Gas Prices
D:Clean Fuel of Choice
E:Disadvantages of Natural Gas
F:Natural Gas Consumption

共用题干
Natural Gas

1 Natural gas is produced from reservoirs deep beneath the earth's surface. It is a fossil fuel（矿物燃
料）,meaning that it is derived from orgaiiic material buried in the earth millions of years ago.The main corn-
ponent of natural gas is methane（甲烷）.
2 The popularity and use of clean natural gas have increased dramatically over the past 50 years as
pipeline infrastructure（基础设施）has been installed to deliver it conveniently and economically to millions
of residential,commercial and industrial customers worldwide.Today,natural gas service is available in all 50
states in the U.S.,and is the leading energy choice for fueling American homes and industries.More than 65
million American homes use natural gas.In fact,natural gas is the most economical source for home energy
needs,costing one-third as much as electricity.In addition to heating homes,much of the gas used in the
United States is used as a raw material to manufacture a wide variety of products,from paint,to fibers for
clothing,to plastics for healthcare,computing and furnishings.Natural gas is also used in a significant number
of new electricity-generating power plants.
3 Natural gas is one of the safest and cleanest fuels available. It emits（发出）less pollution than other
fossil fuel sources. When natural gas is burned , it produces mostly carbon dioxide（二氧化碳）and water va-
por一the same substances emitted when humans breathe.Compared with some other fossil fuels,natural gas
emits the least amount of carbon dioxide into the air when combusted（燃烧）一making natural gas the clea-
nest burning fossil fuel of all.
4 The United States consumes about one一third of the world's natural gas output,making it the largest
gas-consuming region in the world.The U.S.Department of Energy Information Administration forecasts that
natural gas demand will grow by more than 50 percent by 2025.
5 There are huge reserves of natural gas beneath the earth's surface.The largest reserves of natural
gas can be found in Russia , West and North Africa and the Middle East. LNG（液化天然气）has been pro-
duced domestically and imported in the United States for more than four decades.Today,the leading import-
ers of LNG are Japan,Korea,France and Spain.

Paragraph 3__________
A:Popularity and Use of Natural Gas
B:Natural Gas Reserves and Supply
C:Natural Gas Prices
D:Clean Fuel of Choice
E:Disadvantages of Natural Gas
F:Natural Gas Consumption

Primer on Smell
In addition to bringing out1 the flavor of food, what does the sense of smell do for us ?
Smell “gives us information about place, about where we are,” says Randall Reed, a Johns Hopkins University professor whose specialty is the sense of smell. ___1___ “Whether we realize it or not, we collect a lot of information about who is around us based on smell,” says Reed.
Even at a distance, odors can warn us of2 trouble — spoiled food, leaking gas, or fire. “It’s a great alert,” offers Donald Leopold, a doctor at Johns Hopkins. For example, if something in the oven is burning, everyone in the house knows it.
With just a simple scent, smell can also evoke very intense emotion. Let’s say, for example, that the smell is purple petunias. ___2___ Now let’s imagine that your mother died when you were three, and she used to have a flower garden. You wouldn’t need to identify the smell or to have conscious memories of your mother or her garden. You would feel sad as soon as you smelled that spicy odor.
Compared with3 animals, how well do people detect smelts ?
That depends on what you mean by “how well”. We are low on receptor cells ： current estimates say that humans have roughly five million smell-receptor cells, about as many as a mouse. ___3___
Reed says that, across species, there is a relatively good correlation between the number of receptor cells and how strong the sense of smell is. “You can hardly find the olfactory bulb in a human brain —— it’s a pea-sized object. In a mouse, it’s a little bigger. It’s bean-sized in a rat, about the size of your little finger in a rabbit, and the size of your thumb in a bloodhound.”
Does that mean that our sense of smell is not very acute ?
Not exactly. While we may not have the olfactory range of other creatures, the receptors we do have are as sensitive as those of any animal. ___4___ A trained “nose”, such as that of a professional in the perfume business, can name and distinguish about 10,000 odors. Reed says that a perfume expert can sniff a modem scent that has a hundred different odorants in it, go into the lab, and list the ingredients. “In a modest amount of time, he comes back with what to you or me would smell like a perfect imitation of that perfume. It’s amazing.”
What happens to4 our sense of smell as we age ?
Many people continue to have good olfactory function as they get older. ___5___ Leopold says that smell is generally highest in childhood, stays the same from the teens through the 50s, and drops starting at about 60 for women and 65 for men. “The average 80-year-old is only able to smell things half as well as the average 20-year-old,” says Leopold.

词汇：
scent /sent/ n. 气味，香味
petunia /p 'tju:ni / n. 喇叭花
olfactory / l'f kt( )ri/ adj. 嗔觉的，味道的
sniff /snif/ v. 嗅，闻，用力吸

注释：
1. bring out：使……显出，使……变得明显
2. warn of：发出关于……的警告。warn sb. of sth.：警告某人某事
3. compare with：与……相比
4. happen to：发生于，发生在

练习：
A These flowers have a rich spiciness that no other petunia has.
B Odors, or smells, can warn us about trouble.
C That’s not the rule, however.
D And smell tells us about people.
E We can also think, and we make conscious (and successful) efforts to tell the difference between one smell and another.
F A rat has some 10 million, a rabbit 20 million, and a bloodhound 100 million.

The brain finds it best to keep smell receptors（ ）for unfamiliar and emergency signals such as the smell of smoke,which might indicate the danger of fire.

A.available
B.reliable
C.identifiable
D.suitable