巨大的商代司母戊大方鼎可以证明我国商周时期（   ）

$\begin{array}{c}\frac{a_1+a_2}{2}\ge \sqrt{a_1{a}_2}\\ \frac{a_1+a_2+a_3}{3}\ge \sqrt[3]{a_1{a}_2{a}_3}\\ \frac{a_1+a_2+a_3+a_4}{4}\ge \sqrt[4]{a_1{a}_2{a}_3{a}_4}\\ \cdots \cdots \cdots \end{array}$  

照此规律，当 $n\in N^{+}\left(n\ge 2\right)$  时， $\frac{a_1+a_2+a_3+\cdots +a_n}{n}\ge$ ____．

如图，在平面直角坐标系中，已知B（8，0），C（0，6），P（﹣3，3），现将一直角三角板EPF的直角顶点放在点P处，EP交y轴于N，FP交x轴于M，把△EPF绕点P旋转：

阅读下面短文，从短文后所给的A、B、C、D四个选项中选出能填入相应空白处的最佳选项。

Dear Sally,

    How are you? I'm happy that you can do the things you 1 at home. I never have fun, because there are too many 2 in my family. My parents are strict. I have to 3 at six o'clock every morning. And I have to make my bed 4 before breakfast and then go to school. I can't play with my friends after school. I have to do 5homework. After dinner I have to take the dog for 6 walk in the park. I can't watch TV on school nights. I have to 7 the violin for an hour. I can't go to bed late. I have to be in bed 8 nine o'clock. On weekends I have to clean my room and 9the dishes. I also have to go to learn the violin on Sundays. I'm 10 tired. Can you help me?

Yours,

Lisa