A dolphin is sort of large, hope it hepls
Answer:
As the river erodes the landscape in the upper course, it winds and bends to avoid areas of hard rock. This creates interlocking spurs, which look a bit like the interlocking parts of a zip. When a river runs over alternating layers of hard and soft rock, rapids and waterfalls may form.
I believe the answer would be 12, are there any more numbers?
