Iii-eneral sciencewhich of these is the best explanation of how a smooth round stone became smooth? a continuous freezing and thawingbvolcanic actioncit fell off the side of a cliffdit was in a stream for a long time.

D. It was in a stream for a long time

Explanation:

The streams have big influence with their water over the shape of the rocks in them. If there are rocks in the streams, as it usually does, the rocks are constantly under the erosive pressure of the water. The water manages to take small particles out of them, but also moves them along the stream floor. With the movement, the rocks make circular movements. Over time, this type of movement of the rocks because of the water makes them rounded and they look like they have been polished, thus they are also very smooth. Apart from the streams, rocks with this shape can be found also at places that had streams and rivers in the past, so we can even encounter them at places that are now forests, or arid areas, witnessing for the past of those areas.