听力原文： Are electric cars the wave of the future? Automobile manufactures are under pressure to develop cars that do not pollute. One powerful motive is a California law requiring that by the year 2000, 10% of new car sales in the state be so-called 'zero emission vehicles'. These cars must put no pollution, whatsoever, in the atmosphere. California is a huge market for the automobile companies. So they are working hard to meet the standards. So far, the electric car seems to be the best alternative. So the big advantage of the electric cars is that they don't pollute. However, there will be a competition with gas-powered cars and that's where the weaknesses come out. The big problem is that the batteries that power electric cars weigh a lot relative to the amount of power they deliver. For instance, in one prototype electric car, the batteries weigh 400 kilograms and they provide enough energy to go 250 kilometers before recharging, which takes 8 hours. Compare that to a moderately fuel-efficient conventional car, it can go 600 to 700 kilometers on a tank of gas and refilling takes just minutes. If there are other drains on the electric cars' batteries besides the motor, headlights, air-conditioning or heater, its already limited range would be significantly reduced. So, automobile engineers are trying to make more powerful batteries that would increase the cars' range and make them more attractive to buyers. (33)