一质量为m、电阻为r的金属杆ab，以一定的初速度v₀从一光滑平行金属导轨底端向上滑行，导轨平面与水平面成30°角，两导轨上端用一电阻R相连，如图所示，磁场垂直斜面向上，导轨的电阻不计，金属杆始终与导轨接触良好，金属杆向上滑行到某一高度之后又返回到底端时的速度大小为v，则金属杆在滑行过程中（   ）

从1到10的中位数是（　　）　

    My name is Tom. I come from England. I like to have friends who are different from me. My best friend is Paul. Paul is funnier, more outgoing and athletic than me. He always tells jokes and makes me laugh. We also like different things. He likes going to the movies. He likes playing sports. He likes pop music. But I like reading books. He often asks me to go to the movies and gives me some interesting books. And I often give him CDs. We often help each other.