Pour a bucket a sand through the air. Pour water over a pile of sand. Filter sand through a screen into water. Blow on a pile of sand through a straw.
What is the best way to model the effect of wind on sand dunes?

Options:
- Pour a bucket a sand through the air.
- Pour water over a pile of sand.
- Filter sand through a screen into water.
- Blow on a pile of sand through a straw.

Blow on a pile of sand through a straw.