Our school is on Guangming Street. It's next to the People's Library. There is a park across from our school. The pay phone is between our school and a post office. Our school is very beautiful. There are many trees and flowers in it. If you want to come to our school from the airport, take a taxi and go down Center Avenue. You can see a big restaurant on your right. There is a bridge near the restaurant. Go across it and turn left. Then go down Bridge Street. Turn left at New Park and go down Guangming Street. Our school is across from a bank.

已知x，y的取值如下表所示：

如果y与x呈线性相关，且线性回归方程为$\stackrel{\wedge }{y}$=bx+$\frac{13}{2}$，则b=（　　）

已知椭圆E： $\frac{x^2}{a^2}+\frac{y^2}{b^2}$ =1（a＞b＞0）的离心率为 $\frac{\sqrt{3}}{2}$ 直线MN与圆x²+y²= $\frac{4}{5}$ 相切，M（a，0），N（0，b）

（Ⅰ）求E的方程；

（Ⅱ）若E的右焦点为F，圆x²+y²=1的切线AB与E交于A，B 两点（A，B均在y轴右侧），求证：△ABF的周长为定值，并求△ABF的内切圆半径的最大值．