1665年英国科学家罗伯特·   ____    首先发现了细胞——他主要看到的是      ____   。

    I am a student. I like sports. I run every morning and I swim twice a week(一周两次). I like all kinds of ball games. I like football, basketball, volleyball, tennis and ping­pong. I am good at playing ping­pong. I often play ping­pong with my friend, Li Lei. We are on the school team. But he doesn't like any other ball game. He also likes to collect(收集)balls. He has a great collection(收藏品)of balls. He has 60 footballs, 16 volleyballs and many ping­pong balls. We like to watch sports on TV.

在北京的打工妹石芳丽骑电动车经过一个路口时，将76岁老人韩健撞倒。石芳丽立即送老人就医，并辞去工作，专心陪护老人。最终，老人不仅放弃了追责和索赔，还让其家人帮助石芳丽找到了一份新工作。他们的行为启示我们要（  ）

①热爱生活，自尊自爱            ②坚持正义，敢于负责

③宽以待人，乐于助人            ④平等待人，学会分享

计算（先化简，再求值）： $(\frac{3a-1}{a^2-1}-\frac{2}{a+1})÷\frac{1}{a^2-2a+1}$ ，其中a= $\sqrt{2}+1$ ．