Question 13 is based on the conversation you have just heard.

W: What does the term “alternative energy source” mean?

M: (13)When we think of energy or fuel for our homes and cars, we think of petroleum, a fossil fuel processed from oil removed from the ground, of which there was a limited supply. But alternative fuels can be many things. Wind, sun and water can all be used to create fuel.

W: Is it a 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 that it is being produced over time. The real controversy surrounding the mass petroleum we have is how much we need to keep in reserve for future use. (14)Most experts agree that by around 2025, the 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’ll 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: (15)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 into the ground for a long time, which leads to some long-term negative effects, like global warming and green house effect.

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

解析：四个选项都是表示能源的概括性总结，推测题目与概念或主旨相关。对话中男士表示一提到能源或燃料，人们通常会想到汽油这种从地下石油中提取的化石燃料。故C选项“从地下石油中提取的燃料”为正确答案。