阅读短文，根据首字母提示填写单词。

      There is nothing more i____ to life than the sun. W____ the sun, all living things on the earth would die. The sun is a star. In the sky there are t____ of stars like the sun. They are as large as the sun and as hot as the sun. At night you can see many stars, but in the day you can o____ see one star-- the sun.

      The sun is much n____ to us than any other star. That is w____ it looks the biggest and brightest of all the stars. The distance (距离) of the sun from the earth is as m____ as 150,000,000 kilometers. Most stars are thousands of light-years a____from the earth.

      Do you know what a light-year is? N____ in the world travels faster than light. It travels 300,000 kilometers per second. And one light-year is the distance that light can travel in one y____.

I always say to myself,“____(学习)harder and harder!”

生活中纸有哪些用途？（至少写3种） 

已知椭圆$\frac{x^2}{a^2}$+$\frac{y^2}{b^2}$=1（a＞b＞0）的离心率为$\frac{\sqrt{3}}{2}$，且过点（$\sqrt{2}$，$\frac{\sqrt{2}}{2}$）．

（1）求椭圆方程；

（2）设不过原点O的直线l：y=kx+m（k≠0），与该椭圆交于P、Q两点，直线OP、OQ的斜率依次为k₁、k₂，满足4k=k₁+k₂，试问：当k变化时，m²是否为定值？若是，求出此定值，并证明你的结论；若不是，请说明理由．