When General Motors' electric buses hit New York City's streets for a test run a couple of years ago, the company found that the new hybrid vehicles-propelled by a diesel generator and electric motors-burned less than half the fuel of a conventional diesel and created 90 percent less pollution. One hitch: the roughly 5,000 dollars' worth of batteries that mediated the flow of electricity between the generator and motor burned out after only a year. Now, GM plans to keep its hybrid buses rolling by replacing the batteries with a high-tech cousin of the capacitors that regulate power in electronic devices. The same technology may soon help make hybrid cars more efficient and affordable.

Select from the choices above to read the entire article.