An artist went to a beautiful part of the country for a holiday, and stayed with a farmer. Every day he went out with his paints and brushes and painted from morning to evening, and then when it got dark, he went back to the farm and had a good dinner before he went to bed.
    At the end of his holiday he wanted to pay the farmer, but the farmer said, “No, I don't want money… but give me one of your pictures. What is money? In a week it will all be finished, but your painting will still be here.”
T    he artist was very pleased and thanked the farmer for saying such kind things about his pictures. The farmer smiled and answered, “It's not that. I have a son in London. He wants to become an artist. When he comes home next month, I'll show him your picture, and he will not want to be an artist any more, I think. ”

某物体受到一个-6N·s的冲量作用，则下列说法正确的是(   )

甲、乙、丙、丁4种无机化合物均含有2种元素，分子中均含18个电子．甲是气态氢化物，在水中分步电离出两种阴离子．下列推断合理的是（　　）

在学习《政治常识》“公民的政治权利和义务”时，有同学搜索到以下素材：
①某中学生写信给市政府就网吧治理工作提出意见；
②重庆市民协助公安人员抓捕黑社会成员；
③广州市民为2010亚运会建言献策；
④广西一中学生发现某门户网所展示的中国地图上标志的中国领土不完整，当即向该网站的管理者发出电子邮件，指出其错误，要求其更正。
若按权利和义务对以上素材进行分类，正确的是

地理——选修6：环境保护

    互花米草叶片尖锐，原本生长在大西洋沿岸，由于生长密集、地下根茎发达。能够促进泥沙的快速沉降和淤积，加速滩涂变成陆地的进程。上世纪九十年代中旬，互花米草作为“固沙利器”被引入崇明东滩，用作护岸固堤的物种。让人始料未及的是，互花米草却在东濉疯长，排挤海三棱藨草、芦苇等本土生物。

分析互花米草导致崇明东滩鸟类种群数量减少的原因。