中国教育在线讯 2015年上半年大学英语四六级考试于6月13日举行， 中国教育在线外语频道第一时间汇总发布了【英语四级真题及答案 英语六级真题及答案】，供广大考生查阅。

　　W: What does the term alternative energy source mean?

　　M: When you think of energy or fuel for our homes and cars, we think of petroleum or fossil fuel processed from oil removed from the ground of which there is a limited supply. But alternative fuels can be many things, wind, sun and water can all be used to create fuel.

　　W: Is the threat of running out of petroleum real?

　　M: It has taken thousands of years to create the natural stores of petroleum we have now. We are using what is available at a much faster rate than it has been produced over time. The real controversy surrounding the amounts of petroleum we have is how much we need to keep in reserve for future use. Most experts agree that by around 2025 the amount of petroleum we use will reach a peak then production and availability will begin to seriously decline. This is not to say there will be no petroleum at this point, but it will become very difficult and therefore expensive to extract.

　　W: Is that the most important reason to develop alternative fuel and energy sources?

　　M: There're two very clear reasons to do so. One is that whether we have 60 or 600 years of fossil fuels left, we have to find other fuel sources eventually, so the sooner we start, the better off we will be. The other big argument is that when you burn fossil fuels, you release substances trapped in the ground for a long time, which leads to some long term negative effects like global warming and greenhouse effect.

　　13. What do we usually refer to when we talk about energy according to the man?

　　14. What do most experts agree on according to the man?

　　15. What does the man think we should do now?