ASVAB Practice Test

What is the best explanation of how a smooth round stone became smooth?

1. It was eroded by wind

2. It was in a stream for a long time

3. It was polished by hand

4. It was struck by lightning

The correct answer is: It was eroded by wind

The best explanation for how a smooth round stone became smooth is that it was in a stream for a long time. Over time, as water flows over the stone, it causes abrasion and erosion, wearing down sharp edges and rough surfaces. The constant movement of the stone against other particles in the water further contributes to its smoothness. This natural process of river or stream erosion is the primary way stones develop their rounded, smooth shapes, distinguishing it from other methods like man-made polishing or other environmental factors.