$\frac{9}{16}$的算术平方根是____. 　

    Jim, Tom and Tim are in the park. It's a small park, but it's nice. They can see some animals there. There are some birds in the tree. They are yellow. They can fly high. Quack… Quack… What do you hear? Oh，Some ducks. They can swim in the water. There are seven white ducks and nine black ducks. What's that? It's a cat. It's under the tree. It's white. It can jump very fast. The children like the small animals very much.

阅读材料，回答问题。

由于中国人闭关自守、骄傲自满，19世纪三次灾难性的战争使他们受到了巨大的刺激，在这些战争中所遭到的耻辱性失败，迫使中国人打开大门，结束他们对西方的屈尊态度，重新评价自己的传统文明，其结果是入侵和反入侵的连锁反应……                               ──《全球通史》第十六章

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