2014年托福考试精选练习及答案(第七套)_第2页

　　The reading is correct in pointing out the problems associated with oil powered cars. Yes, oil is a finite resource, and yes, burning oil harms the environment. However, the reading is a way too optimistic at the assessment of hydrogen-based fuel-cell engines. Hydrogen is not the solution to these problems.

　　First, hydrogen is not as easily available as the passage indicates. Although it’s present in common substances like water, is not directly usable in that form. For use in a fuel-cell engine, hydrogen must first be obtained in a pure liquids state. This pure liquid hydrogen is a highly artificial substance. It’s technologically very difficult to produce and store liquid hydrogen. For example, it must be kept very, very cold, at minus 253 degree Celsius. Imaging the elaborate cooling technology that’s required for that, so hydrogen’s not such a practically and easily available substance, is it?

　　Second, using hydrogen would not solve the pollution problems associated with cars. Why? Producing pure hydrogen creates a lot of pollution. To get pure hydrogen from water or natural gas, you have to use a purification process that requires lots of energy that obtained by burning coal or oil. And burning coal and oil creates lots of pollution. So although the cars would not pollute, the factories that generate the hydrogen for the cars would pollute.

　　Third, there won’t necessarily be any costs savings when you consider how expensive it is to manufacture the fuel cell engine. That’s because fuel cell engines require components made of platinum, a very rare and expensive metal. Without the platinum component in the engine, the hydrogen doesn’t undergo the chemical reaction that produces the electricity to power the automobile. All the efforts to replace platinum with a cheaper material have so far been unsuccessful.