（Ⅰ）求线性回归方程；

（Ⅱ）估计使用年限为10年时，维修费用是多少？

参考公式： $\widehat{b}=\frac{{\displaystyle \sum _{i=1}^n(x_i-\overline{x})(y_i-\overline{y})}}{{\displaystyle \sum _{i=1}^n{(x_i-\overline{x})}^2}},\widehat{a}=\overline{y}-\widehat{b}\overline{x}$ ．

公民应该如何维护国家安全？（公民应怎样保守国家秘密？）

阅读理解

    My family is not very big. There are only three cats. I'm a white cat. My name is Snow White. My husband (丈夫) is a black cat. His name is Captain Black Cat. We have a pretty (漂亮的) daughter. Her name is Lily. She is black and white. She's two years old. We live a happy life.

    Every day we work hard to catch the mice (捉老鼠).  We help people live a happy life in this house.