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听力原文： Good morning, I'm Michael, housing director here at the university. I'm visiting all the dormitories this week to inform. students about check out procedures. I know you have a lot on your mind with finals coming up, but there are a few things you need to be aware of as you prepare to leave for vacation. This dormitory will be closed during the summer months and will reopen on September 1st. You must vacate your room by June 3rd. Even if you are registered for classes during the summer, you must leave this dorm by June 3rd. If this poses a problem for you, you should contact my office as soon as possible. You should remember to turn in your room key before you leave. Failure to return your key can result in a dollar fine. You must also make sure that all of your personal property has been cleared out of your room. I will be passing out a form. for you to fill out concerning the condition of your room. You should report on the form. of any damage to your room which has occurred over the last year, such as holes ill the room's walls, doors or windows. That way our summer maintenance crew will know where to make re pairs before the next school year starts. If you have any questions during the next few days, please ask your resident advisers or call my office. Now, please take one of the forms as they are passed around.
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According to the text, which of the following is NOT a use for a hydrophone？
Tobago's area is ______.
听力原文： No one knows exactly why we sleep. But scientists have learned a lot about how we sleep, From sleep experiments, scientists have learned that there are four different stages of sleep.
When you first fall asleep, your heart starts to beat more slowly and your breathing slows down. If something wakes you, you might not think that you had been asleep. Some people call this kind of sleep dozing. Scientists call it Stage One sleep. Next, if you are not awakened, you drift into a deeper sleep. Your pulse and breathing become even slower than they were during Stage One sleep. But you can still be awakened quite easily. If you take a cat nap, you probably will not get any further than this stage of sleep, which is called Stage Two.
If you sleep longer than about twenty minutes, you go into the third stage of sleep. Your body is very relaxed. It would take a loud noise to wake you up.
You have probably heard of people who walk in their sleep. No one knows what makes people sleepwalk. But a person can sleepwalk only during Stage Four. This is the deepest kind of sleep. If someone wakes you up during stage four, you might feel very confused. It might take you a few minutes to get used to being awake.
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THE HYDROGEN ECONOMY
It seems-like every day there is a new announcement in the news about automobiles powered by fuel cells. The promises are great, since fuel cells have the potential to very quickly double the efficiency of cars while significantly reducing air pollution.
At the same time, there have been news stories for decades about the problems associated With petroleum. Everything from oil spills to ozone(臭氧) alerts to global warming gets blamed on our dependence on fossil(化石) fuels.
These two forces are leading the world toward what is broadly known as the hydrogen economy. If the predictions are true, over the next several decades we will all begin to see an amazing shift away from the fossil fuel economy we have today toward a much cleaner hydrogen future.
Problems with the fossil fuel economy
While fossil fuels have played an important role in getting society to the point it is at today, there are four big problems that fossil fuels create:
Air pollution--When cars burn gasoline, the internal combustion engine also produces:
Carbon monoxide, a poisonous gas
Nitrogen oxides, the main source of urban smog
Unburned hydrocarbons, the main source of urban ozone
Environmental pollution--The process of transporting and storing oil has a big impact on the environment whenever something goes wrong. An oil spill, pipeline explosion or well fire can create a huge mess.
Global warming—The carbon dioxide coming out of every car's tailpipe is a greenhouse gas that is slowly raising the temperature of the planet. The ultimate effects are unknown, but it is a strong possibility that, eventually, there will be dramatic climate changes that affect everyone on the planet.
Dependence--The United States, and most other Countries, cannot produce enough oil to meet demand, so they import it from oil-rich countries. That creates an economic dependence. When Middle East oil producers decide to raise the price of oil, the rest of the world has little choice but to pay the higher price.
Advantages of the hydrogen economy
The hydrogen economy promises to eliminate all of the problems that the fossil fuel economy creates. Therefore, the advantages of the hydrogen economy include:
The elimination of pollution caused by fossil fuels-When hydrogen is used in a fuel cell to create power, it is a completely clean technology. The only byproduct is water. There are also no environmental dangers like oil spills to worry about with hydrogen.
The elimination of greenhouse gases--If the hydrogen comes from the electrolysis of water, then hydrogen adds no greenhouse gases to the environment. There is a perfect cycle--electrolysis produces hydrogen from water, and the hydrogen recombines with oxygen to create water and power in a fuel cell.
The elimination of economic dependence--The elimination of oil means no dependence on the Middle East and its oil reserves.
Distributed production--Hydrogen can be produced anywhere that you have electricity and water. People can even produce it in their homes with relatively simple technology.
The problems with the fossil fuel economy are so great, and the environmental advantages of the hydrogen economy so significant, that the push toward the hydrogen economy is very strong.
Technological Hurdles(障碍)
The big question with the hydrogen economy is, "Where does the hydrogen come from？" After that comes the question of transporting, distributing and storing hydrogen. Hydrogen tends to be large and tricky in its natural gaseous form.
Once both of these questions are answered in an economical way, the hydrogen economy will be in place.
Where does the hydrogen come from？
There are two possible sources for the hydrogen
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