[填空题]His article on present day economy is (worth) ______ of study.

[填空题]His article on present day economy is (worth) ______ of study.

[简答题] THE HYDROGEN ECONOMY It seems like every day there is a new announcement in the news about automobiles powered by fuel cells. The promises are great, since fuel cells have the potential to very quickly double the efficiency of cars while significantly reducing air pollution. At the same time, there have been news stories for decades about the problems associated With petroleum. Everything from oil spills to ozone(臭氧) alerts to global warming gets blamed on our dependence on fossil(化石) fuels. These two forces are leading the world toward what is broadly known as the hydrogen economy. If the predictions are true, over the next several decades we will all begin to see an amazing shift away from the fossil fuel economy we have today toward a much cleaner hydrogen future. Problems with the fossil fuel economy While fossil fuels have played an important role in getting society to the point it is at today, there are four big problems that fossil