Q:Answer the following question given this paragraph: Mountain streams may erode waterfalls. As shown in Figure below , a waterfall forms where a stream flows from an area of harder to softer rock. The water erodes the softer rock faster than the harder rock. This causes the stream bed to drop down, like a step, creating a waterfall. As erosion continues, the waterfall gradually moves upstream. Q: When a stream flows from a hard to soft rock area, what is often formed? Choices: - a lake - a river - a riverbank - a waterfall A:
A:
a waterfall