按要求完成下列句子。

1. I go to the library once a week. (改写成以he作主语的句子)

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2. He is 154 cm. I'm 160 cm. (用比较级合并成一句话)

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3. My father often cooks meals at home. (对画线部分提问)

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4. Linda saw the animals yesterday. (变为一般疑问句，作肯定回答)

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5. It's going to rain tomorrow. (变为一般疑问句，作否定回答)

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有盐酸和MgCl₂的混合溶液100g，向混合溶液中逐滴加入溶质质量分数为10%的NaOH溶液，生成的沉淀与加入的10%的NaOH溶液质量关系如图所示．若MgCl₂在混合溶液中质量分数为9.5%．求：

（1）A点处溶液中的溶质化学式为______．

（2）恰好沉淀完全时，所得溶液中溶质的质量分数是多少？（结果精确到0.1%）______

（3）C点的坐标（x₁，y₁）中为______．