A、The unrest in North Africa and the Middle East. B、The global economic recession. C、The environmental pollution. D、The increase

Unrest in North Africa and the Middle East has pushed oil prices back into the news. Prices have been rising at their fastest level since 2008. The price of oil affects prices and demand for energy, plastics, farm chemicals and many other products made with petroleum. The United States has a Strategic Petroleum Reserve that contains more than 700 million barrels of oil. But intervening in the market could hurt oil production in the United States.(30)Oil prices have been rising at a bad time, just as many economies have been recovering from the global recession. Also, several countries in the euro area are still struggling with debt crises. European Central Bank President Jean Claude Trichet said last week that "strong vigilance(警惕)" is needed to contain inflation. That could mean raising interest rates which could hurt European countries heavily in debt. In the United States, higher fuel prices come just as General Motors and Chrysler show signs of recovery after their reorganizations. American car sales last month were 27% higher than last February. GM led all carmakers with a 47% increase.(31)High fuel prices reduce demand for big cars and trucks. But economist George Magliano says this time, high prices may be good for carmakers. With gasoline prices higher, certain people might want to get a much more fuel-efficient vehicle and that doesn’t mean even a hybrid or an electric vehicle which they could do. but the gasoline vehicles get 30% better mileage today than they did three or four years ago.
29. What causes the increase of the oil prices?
30. Why does the speaker say oil prices have been rising at a bad time?
31. How does the increase of oil prices affect the car manufactures?