Why is a rivery rich

why is a river rich? Why is a river very rich? Why is a river rich?Because___________ why is a river so rich? (脑筋急转弯)Why is a river rich? 谜语:why is a river so rich? 英语谜语:Why is a river rich? Why is the river rich? What is more useful after it is broken?Why is a river rich?W 英语趣味回答：why is river rich? Why the river is very rich? why the river is so rich