"Why was the river rich?

Why is the river rich? Why the river is very rich? why the river is so rich why is a river rich? 英语趣味回答：why is 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? 两个英语谜语...急 1.why is river rich?2.what letter stand for the o