有关大陆架和大陆坡的说法，正确的是(　　)

为了了解某校中学生中有多少人已经患上近视眼，判断下列选取对象的方案是否恰当？请说明理由．

根据内容完成Sally's family tree.

    I'm Sally, I'm a student in No.14 Middle School. This is my family tree. You can see it is a big family. My father is Jonathan, my mother is Claire. They have three children. My brother's name is William and my sister's name is Olivia. My grandparents Jerry and Elizabeth have two sons. My uncle Mike and my aunt Sarah have a son, his name is Joseph. He is my cousin. He is four years old. We all love him very much.

①____ ②____ ③____ ④____ ⑤____

生态系统具有自我调节能力，所以我们就可以过度地利用它．

抗原和抗体不仅在生物体内发生反应，在体外也能进行反应，研究这种反应的方法之一是用琼脂双重扩散法,这种方法如图1所示。在琼脂片上开两孔，在其中加入抗原和抗体，使其在琼脂中扩散，扩散了的抗原和抗体在一定的位置发生反应。在琼脂中出现可以用肉眼观察到的线，我们把这种线叫沉降线。X和Y表示两种抗原，x和y为相应的抗体，图2中哪一项表示正确的沉降线(     )