概要信息：

Car manufacturers and governments have been eagerly seeking a replacement for the 
automobile's main source of power, the internal-combustion engine. By far the most promising 
alternative source of energy for cars is the hydrogen-based fuel-cell engine, which uses hydrogen 
to create electricity that, in turn, powers the car. Fuel-cell engines have several advantages over 
internal-combustion engines and will probably soon replace them.
One of the main problems with the internal-combustion engine is that it relies on petroleum, either 
in the form of gasoline or diesel fuel. Petroleum is a finite resource; someday, we will run out of oil. 
The hydrogen needed for fuel-cell engines cannot easily be depleted. Hydrogen can be derived 
from various plentiful sources, including natural gas and even water. The fact that fuel-cell engines 
utilize easily available, renewable resources makes them particularly attractive.
Second, hydrogen-based fuel cells are attractive because they will solve many of the world's 
pollution problems. An unavoidable by-product of burning oil is carbon dioxide, and carbon dioxide 
harms the environment. On the other hand, the only byproduct of fuel-cell engines is water.
Third, fuel-cell engines will soon be economically competitive because people will spend less 
money to operate a fuel-cell engine than they will to operate an internal-combustion engine. This is 
true for one simple reason: a fuel-cell automobile is nearly twice as efficient in using its fuel as an 
automobile powered by an internal-combustion engine is. In other words, the fuel-cell powered car 
requires only half the fuel energy that the internal-combustion powered car does to go the same 
distance.