A、20-50 years. B、50-100 years. C、100-120 years. D、200-500 years. C

Stall: Hi, Camellia. Have you attended professor Gabriel’s lecture?
Camellia: No. What was it about?
Stall: Energy -- energy future and today.
Camellia: Oh, what a pity. You know, I’m writing a paper on this subject. And I have spent a lot of time to collect materials. I shouldn’t have missed this chance.
Stan: Don’t worry. I made a lot of notes. You can take my notebook and have a look.
Camellia: It’s very kind of you... (open the notebook).., mmm.., but it seems.., mmm.., that you have written hastily and some parts are not...
Stall: That’s true. The lecture is magnificent, so I tried to write down all the things.., mmm.., never mind. I’m free now and I can tell you what I can remember.
Camellia: Oh, thank you. You’re really a great friend.
Start: OK. The professor began with the alternative energy. He said there is a great deal of information and enthusiasm about the development and increased production for the global energy needs from alternative energy sources.
Camellia: I know that solar energy, wind power and moving water are all sources of alternative energy.
Stan: And they are progressing, wind power and moving water are all sources of alternative energy.
Camellia: It’s not so?
Start: According to the professor, absolutely not. We often mention alternative energy to refer to those energy that is produced from sources other than our primary energy supply: fossil fuels -- coal, oil and natural gas. The problem is, fossil fuels are non-renewable.
Camellia: Yes, you know, fossil fuels were formed from plants and animals that lived hundreds of millions of years ago. So there would be another hundreds of millions of years to reproduce.
Start: They are limited in supply and we have mostly depended on them for our energy needs, from home heating and electricity to fuel for our automobiles and mass transportation. They will one day be used up. There is no escaping this conclusion.
Camellia: How about nuclear energy. Isn’t it a potential source of energy?
Start: The professor said nuclear energy, which is primarily generated by splitting atoms, only provides 6% of the world’s energy supplies. And it is not likely to be a major source of world energy consumption because of public pressure and the relative dangers associated with unleashing the power of the atom.
Camellia: Did the professor give any information about how much fossil energies provide?
Stall: Let me see...ah, yes, that’s nearly 88% of the world’s energy needs, or about 350 quadrillion British Thermal Units -- or BTUs. The total world energy demand is about 400 quadrillion BTUs -- each year. A BTU is roughly equal to the energy and heat generated by a match. Of this amount oil, coal and natural gas supply, oil is the king, providing about 41% of the world’s total energy supplies, or about 164 quadrillion BTUs. Coal provides 24% of the world’s energy., or 96 quadrillion BTUs, and natural gas provides the remaining 22%, or 88 quadrillion BTUs.
Camellia: Just how limited are our fossil fuel reserves?
Stan: Some estimates say our fossil fuel reserves will be used up within 50 years, while others say it will be 100-120 years.
Camellia: It’s terrible. We are going to run out of fossil fuels for energy and we have no choice but to prepare for the new age of energy production since, most certainly, human demands for energy will not decrease.
Start: Nobody really knows when the last drop of oil, lump of coal or cubic foot of natural gas will be collected from the Earth. All of it will depend on how well we manage our manage our energy demands and how well we can develop and use renewable energy sources.
Camellia: I think the development and use of sun, wind and water is a good way. They are perfect energy sources. They are non-polluting, renewable and efficient. They are simple: all you need is sunlight, running water and wind.
Start: But the development takes time. In fact, according to what the professor said, there exists a Fossil Fuel Dilemma. Fossil fuels exist, and they provide a valuable service. The key is not that the use of fossil fuels for energy is problematic, but it’s the side effects of using them that cause all of the problems. Burning fossil fuels creates carbon dioxide, the number one greenhouse gas contributing to global warming. Combustion of these fossil fuels is considered to be the largest contributing factor to the release of greenhouse gases into the atmosphere. In the 20th century, the average temperature of the Earth rose one degree Fahrenheit.
Camellia: Is there any solution?
Start: At the end of his lectures, I remember, the professor said, "No single solution can meet our society’s future energy needs. The solution instead will come from a family of various energy technologies that share a common thread -- they do not use up our natural resources or destroy our environment."
Camellia: Oh, Stan, you have helped me so much. I think I need to revise some parts of my paper. Oh, thank you so much.