Extra
“Anyone who believes exponential growth can go on forever in a finite world, is either a madman or an economist.” ~Kenneth Boulding, Economics professor
If you want to know more about the state of energy resources in the world in general (and specifically in the US), you can have a look at the video - called "Arithmetic, Population and Energy" - linked below. It's probably not really the most important video you'll ever see, but it's still pretty interesting. However, it's over an hour long (it comes in 8 parts, the link to the following part is always under the video window), so only watch it if you have nothing else to do for a while ;-) It also has quite a few conditionals and comes with visual support, so you might use it to practise your English skills.
It's not homework, it's just for people who are interested.
