I agreed with wang zi

"The world will run out of oil around 2050 the closer we get to this day without another alternative energy source the more the price will go up." quote from wang zi.

I agree that sentense.It's true. The petrol is going to run out soon as the people using petrol increase and increase day by day. That why nowadays the sciences keep on search and experiment for the alternative energy. We really need another energy source if the petrol is really completely used.If not, we'll go back to the past again.