阅读下面的三则材料，联系本文，写出你探究的结果。

材料一:两千多年前，黄河只叫“河”，没有“黄”早。《诗经》中许多篇章都提到过。那时的黄河水还比较清亮。黄河上游及晋陕一带森林植被还比较多，水草丰茂，清澈秀丽。

材料二:古人言“黄河清，天下宁”，黄河的治理，事关广大人民的生计。

材料三:

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下列（  ）假说被“日心说”理论排除。

Dear Dad，
   Happy birthday to you !
   On this special day I'd like to talk to you1a special way．
   I don't think I am good at2you my thought face to face with you，so I'm writing to show my deep love for you．You're not a rich man or a famous person．But in my heart，you are one of the greatest3 in the world．I am4 you．
   You are5 interested in fame and wealth．You do6 things like paying phone bills on time，and working as a worker in your factory．The smile on your face shows you are pleased with the family．You take good care of my grandparents．You help me with my schoolwork and do some shopping with Mom on Sundays．
   In the past，I didn't care7 you were with me or not．Now I am sorry to say I8 you the respect before．But I am thankful for what you have done for me． I am quite lucky that I have9 a great father．And I feel happy that now I can let you10 how much I love you．You are successful as a son，a husband，a father，and a friend．
   Wish you happy forever!
                                                                                                                                               Yours，

                                                                                                                                               David