已知双曲线C： $\frac{x^2}{a^2}-\frac{y^2}{b^2}$ =1（a＞0，b＞0）的左、右焦点分别为F₁，F₂，O为坐标原点，点P是双曲线在第一象限内的点，直线PO，PF₂分别交双曲线C的左、右支于另一点M，N，若|PF₁|=2|PF₂|，且∠MF₂N=120°，则双曲线的离心率为（   ）

从“充分条件”“必要条件”中选出适当的一种填空：

①“ 有实根”是“ ”的____；

②“ ”是“ ”的____．

    I learned how to accept life as it is from my father.1. he did not teach me acceptance when he was strong and healthy, but rather when he was2and ill .
    My father was3a strong man who loved being active. But a terrible illness4all that away. Now he can no longer walk. And he must sit quietly in a chair all day. Even talking is5. One night, I went to visit him with my sisters. I told them about one of my beliefs. I said that we must very often give things up6we grow our youth, our beauty, our friends, but it always7that after we give something up，we gain something new in its place. Then suddenly my father spoke up, “But, Peter, I gave up8!What did I gain?” I thought and thought, but I could not think of anything to say. 9he answered his own question: “I10the love of my family.” I looked at my sisters and saw tears in their eyes along with hope and thankfulness.
    I was also11by his words. After that, when I began to feel irritated (恼怒的) at someone, I would remember his words and become12. If he could replace his great pain with a feeling of love for others, then I should be13to give up my small irritations. In this14，I learned the power of acceptance from my father.
    Sometimes I15what other things I could have learned from him if I had listened more carefully when I was a boy. For now, though I am grateful for this one gift.

坐在温馨的物理考场，仔细想想：你平时走路的步幅约为50____，上体育课时你跑100m所需时间约为16____（填上合适的物理量单位）．