细胞学说揭示了（  ）  

将下列陈述句改成反问句

①生活富裕了，我们也不能铺张浪费。

②我们不能忘记妈妈的爱。

从某学校的800名男生中随机抽取50名测量身高，被测学生身高全部介于155cm和195cm之间，将测量结果按如下方式分成八组：第一组155，160），第二组160，165），…，第八组190，195，右图是按上述分组方法得到的频率分布直方图的一部分，已知第一组与第八组人数相同，第六组的人数为4人．

（Ⅰ）求第七组的频率；

（Ⅱ）估计该校的800名男生的身高的中位数以及身高在180cm以上（含180cm）的人数；

（Ⅲ）若从身高属于第六组和第八组的所有男生中随机抽取两名男生，记他们的身高分别为x，y，事件E={|x﹣y|≤5}，事件F={|x﹣y|＞15}，求P（E∪F）．

   The best way of learning a language is using it .The best way of learning English is talking in English as much as possible. Sometimes you'll get your words mixed up ( 混合)and people will not understand you .Sometimes people will say things too quickly and you can't understand them. But if you keep your sense of humor (幽默感),you can always have a good laugh at the mistakes you make(你所犯的错误). Don't be unhappy if people seem to be laughing at your mistakes（错误）. It is better for people to laugh at your mistakes than to be angry with you. because they don't understand what you are saying .The most important thing for learning English is : “Don't be afraid of making mistakes because everyone makes mistakes. ”