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    An elephant and a monkey were arguing.

  “Look, how big and strong I am!” The elephant said.

    The monkey disagreed, “Look, how fast I can run and climb! Can you?”

    At last they asked a wise tiger, “Which is better—to be strong or to be quick?”

    The tiger said, “Go across the river and pick the fruit on that tree for me, then I can tell.”

    So they went to the river, but the water ran fast and the monkey was afraid.

“Get on my back,” said the elephant proudly, “I shall carry you.”

Soon they crossed the river. There stood the tree. But the fruit was too high for the elephant to reach. He also tried to pull the tree down, but failed.

  “Don't worry.” The monkey climbed quickly up the tree, and picked the fruit.

    Then they returned and gave the tiger the fruit. “Which is better—to be strong or to be quick?”

The tiger smiled, “Neither of you could get the fruit alone. It took both the elephant's strength and the monkey's quickness to get it.”

“一般不用K、Ca、Na等活泼金属来置换盐溶液中的其他金属元素”，这是教科书上的一句话。 小科对此进行了思考，并查阅资料，对金属钠和硫酸铜溶液的反应进行探究。

【查阅资料】钠常温下就能与水发生剧烈反应，反应方程式为:2Na+2H₂O==2NaOH +H₂↑。

【提出猜想】猜想一:金属钠和硫酸铜溶液反应会有铜生成。

猜想二:金属钠和硫酸铜溶液反应，生成的沉淀只有氢氧化铜。

【实验及现象】切取不同大小的钠块分别投入到两种不同浓度的硫酸铜溶液中，有关产生沉淀

的现象如下表所示。

小科咨询老师后得知蓝绿色沉淀为碱式铜盐。