“胜日寻芳泗水滨，无边光景一时新．等闲识得东风面，万紫千红总是春．”在此美丽盛景中，蝴蝶将一株油菜的花粉带到另一株油菜花的柱头上后，即可发生花粉萌发、花粉管伸长、释放精子、精卵融合等一系列生理反应；若将一株油菜的花粉带到一朵桃花的柱头上则不会发生这一系列反应．该现象能很好地说明细胞膜（　　）

      Everyone likes living in a clean and comfortable environment. If the envionment(环境) is bad, it will affect（影响）our bodies, and make us not feel well. Sometimes we may be terribly ill. At that time we don't want to work, and we have to stay in bed and rest at home. So the envrionment is very important to us.
      It's germ that makes us ill. There are germs everywhere, They are very small and you can't find them with your own eyes, but you can see them with a microscope（显微镜）. They are very small and there may be hundreds of them on a very small thing, Germs can always be found in the dirty water. When we look at dirty water under the microscope, we shall see them in it. Germs can also be found in air and dust（灰尘）. If you cut your finger, some of the dust from the floor may go into it, and you will have much pain in it. Sometimes the germs will go into all of your boby, and you will have pain everywhere.
     To keep us healthy, we should try to our best to make our environment become cleaner and tidier. This needs us to act together.

阅读下列材料:

材料一 西周时,耒、耜是主要农具,“一人跖(踏)耒而耕,不过十亩”。战国时,李悝说:“今一夫挟五口,治田百亩,岁收亩一石半,为粟百五十石。”

材料二 中国农村原本是一个自治的社会,“皇权不下县,县下是宗族,宗族皆自治,自治出于伦理”,几千年来都是如此。广大农民“交了粮,自由王”,强制他们的力量也并不多。相反,小农们对封建国家有很强的约束力,直接决定着社会的治乱、经济的衰荣。——李成贵《国家、利益集团与三农困境》

请完成:

①主要成分是纤维素和果胶  ②具有支持、保护作用  ③具有选择透过性  ④不属于细胞结构