已知函数f（x）=x³对应的曲线在点（a_k，f（a_k））（k∈N^*）处的切线与x轴的交点为（a_k+1，0），若a₁=1，则$\frac{f\left(\sqrt[3]{a_1}\right)+f\left(\sqrt[3]{a_2}\right)+\cdots +f\left(\sqrt[3]{a_{10}}\right)}{1-{\left(\frac{2}{3}\right)}^{10}}$=____ 

太阳辐射的纬度变化导致地球上（　　）                                          

三角形两边长分别为3和6，第三边是方程x²-6x+8=0的解，则这个三角形的周长是（     ）

A: Morning, Tom. You don't look well. ____?

B: Well, I have got a cold. But it's not serious. Hey, Jack, did you see the movie on CCTV 6 last night?

A: No, I didn't. ____?

B: Harry Potter Ⅲ. It was so exciting. So, what were you doing at that time?

A: ____. I'm not good at English, you know.

B: But English is not very hard to learn. ____.

A: Thank you for your advice. ____?

B: It's nearly 7:50. Hurry up, or we'll be late fir school.