Mr. Lin has a store. It's next to No. 5 Middle School. It sells maps, books, pens, pencils, clothes and some other things. The things in his store are not expensive. Boys and girls like to go to his store. They like Mr. Lin because he is very nice. Mr. Lin likes the boys and girls, too. Mr. Lin has a “lost and found” box in his store. Look! A baseball, a ruler and some books are in the box. This box helps some boys and girls find their lost things. A sofa is in Mr. Lin's store, too. Boys and girls can sit there and read books after school. They can ask Mr. Lin questions about these books and he often helps them to find the answers.

地球上昼夜交替现象产生的原因是（  ）

中国的戏曲发展有着悠久的历史和灿烂的文明，到了明清时期，全国各地形成了各具特色的地方戏，如安徽的徽剧、云南的昆剧湖北的汉剧等等，后来徽剧与汉剧相互融合，兼收昆曲、秦腔以及其他民间曲调的唱腔、剧目和表演方式，形成的一个新剧种。请问这个新剧种是（    ）

已知实数x，y满足$\left\{\begin{array}{c}2x+y-2\ge 0\\ x-2y+4\ge 0\\ 3x-y-3\le 0\end{array}\right.$，则x²+y²的最大值为____ ．