One example of Supply and demand is A. Clean air. B. Oil. C. Plastic or D. Democracy
Which one?

there are so many examples for that in different areas, like biology experiment carried out in our lab recently.

here's one link:

glacial erosion, the picking up and movement of earth beneath a glacier, is also referred to as plucking. erosion and transportation of individual pieces of bedrock, especially large "joint block occur as a result of this glacial erosion. plucking is type of erosion in which rocks become frozen into the bottom and sides of the glacier.as the glacier moves downhill it 'plucks' the rocks frozen into the glacier from the ground.