Riddle: What flattens all mountains, wipes out all species, destroy every building, and turns everything into pieces?
Answer: Time flattens entire mountains with erosion. Erosion is the work of surface treatments (such as water flow or wind) that move soil, rock or dissolved material from one place in the Earth’s crust to another. In this way, as time went on, the mountains became flat.
Species have a certain lifespan. It is possible for them to live forever. It is the same for buildings. They ruin it as time goes on.
So, the correct answer is time.