They have the shapes of the minerals from which they are made. They were smoothed by the action of wind and water. They were squeezed up through the soil. They hardened in rounded pockets of soil.
I gave my students this multiple choice question: Why are some rocks smoother and rounder than others?

Only one answer is correct among these 4 choices:
- They have the shapes of the minerals from which they are made.
- They were smoothed by the action of wind and water.
- They were squeezed up through the soil.
- They hardened in rounded pockets of soil.

Could you tell me which one is correct?

They were smoothed by the action of wind and water.