A lot of people like sports. And some love 1 very much. An elephant can also 2basketball. There is an elephant. Its 3is Toktak. He 4 strong and cute. Many people like 5. Do you know 6? Because 7his free time, Toktak often plays basketball with his long trunk（象鼻）. He 8the sport very much. The basketball looks like a toy to Toktak. It is 9to watch Toktak playing basketball. Do you like the elephant? Let's 10him in the zoo. I think you can have fun there.

在光滑水平面上，a、b两小球沿水平面相向运动．当小球间距小于或等于L时，受到大小相等，方向相反的相互排斥恒力作用，小球间距大于L时，相互间的排斥力为零，小球在相互作用区间运动时始终未接触，两小球运动时速度v随时间t的变化关系图象如图所示，由图可知（   ）

观察下列顺序排列的等式：

9×0+1=1

9×1+2=11

9×2+3=21

9×3+4=31

9×4+5=41

…

根据数表所反映的规律，猜想：第n个等式（n为正整数）应为（　　）

美国形成最早的工业区在