1)What is an origin of the wind? Explain.
2)What is acid rain? Explain.
3)What is an origin of ground water? Explain.
4)What is the water cycle? Explain.
5)What is a source if the salts?
6)If fresh water flows out to the sea, why is the sea still salty?
7)What is a wave? Explain.
8)What is an ecosystem?