已知a＞0，b＞0，且a²+b²= $\frac{9}{2}$ ，若a+b≤m恒成立，

（Ⅰ）求m的最小值；

（Ⅱ）若2|x﹣1|+|x|≥a+b对任意的a，b恒成立，求实数x的取值范围．

把肯定句改成双重否定句

①如果我们选择居住，就要考虑适合的条件。

②他会迟到的。

      It was the first day of biology class. The teacher wanted to give a good1  to his class. He wanted to  2  his students’ eyes to the world of biology.
      He knew that 3  young students was not easy, so he worked 4  and tried to find a good way to teach this class.5  thinking for a long time, he made a 6  at last. He decided to show the kids something7 and teach them a lesson at the same time.
      He asked his students to 8  carefully. Then he began. He put a worm(虫子) into a glass of water. The worm 9 around in the water. Then he put a second worm into a glass full of alcohol(酒精). It died at once. He asked the students if anyone knew about 10 they learned from it. A boy said, “You showed us that if we drink alcohol we won't have worms.”

化学和生产、生活密切相关，请你用所学知识回答下列问题：

（1）空气属于____ （选填“混合物”或“纯净物”），雾霾天气是空气受到严重污染造成的，空气污染物主要有____ 与粉尘两大类．

（2）人类离不开水，自然界中的水都不是纯水，利用沉淀、____ （填操作方法）、吸附和蒸馏等方法可以净化水，实验室可以用电解水实验探究水的组成．

（3）锅里的油一旦着火，可用锅盖盖灭，其原理是____ ．

（4）目前，襄阳市区所有的出租车和大部分公交车使用的燃料都是天然气，天然气的主要成分是____ ．

（5）铁是应用最广泛的金属，铁制品很容易生锈，实验室可以用稀盐酸除去铁锈，该反应的化学方程式为　____ ．

（6）家庭用的铝壶由于长时间烧水，内壁有一层白色水垢（主要含碳酸钙），在家里可选用____ 除垢．

（7）电线外面包了一层绝缘体，它的成分是聚氯乙烯，它属于____ 材料．

（8）膨化食品常采用充气包装，充入的气体可能是____．