儿童一旦缺钙，容易患（    ）

①请以“难忘的________”为题，写出你对老师、同学的感激与留恋，写出对校园生活的依依不舍。

②或写一个离别欢送的场面，比如毕业典礼，师生话别。任选一题，中心突出，语言生动，情真意切。500字左右。

已知P是以F₁、F₂为焦点的椭圆$\frac{x^2}{a^2}+\frac{y^2}{b^2}=1\left(a>b>0\right)$上一点，若$\overrightarrow{P{F}_1}·\overrightarrow{P{F}_2}$=0，$\tan \angle P{F}_1{F}_2$=2，则椭圆的离心率为（   ）

    This is a meaningful and impressive story. A man came to the USA. After settling down at ____island, he went into a cafeteria to get something ____ (eat). He sat down at an empty table ____ (silent) and waited for someone to take his order, ____ nobody did. Finally, a woman with a plate full of food ____ (sit) opposite him and informed him ____ the cafeteria worked. “Start out at that end,” she said. “Just go along the line and pick out what you want. At the other end, they'll tell you how much you have to pay.”

    “I soon learned how everything worked in the USA,” the man told a ____ (rely) friend. He said, “Life's a cafeteria here. You can get anything as long as you are ____ (will) to pay the price.”

    You can even get success, but you'll never get it if you wait for someone to bring it to you. You have to get up and get it ____ (you). You can't change the things that you can't avoid or prevent. The only thing you can do is control your attitude. Once you reach that point in life, ____ (achieve) won't be too far away.