Many types of energy are harnessed to create electricity. Wind and solar power are examples of renewable sources, but petroleum is non-renewable. What fact explains why petroleum is considered non-renewable?
A) Petroleum can only be generated from dinosaur excrement.
B) Petroleum is manufactured from an element that no longer exists.
C) Petroleum is only found in Saudi Arabia and they may refuse to sell to other countries.
D) Although petroleum is a fossil fuel, created from plant and animal remains, the process takes many millions of years.