根据短文理解，选择正确答案。

    Do you know pigeons? They are a kind of birds. They are in white and grey. Some people say they are not beautiful but they are cute and smart. Many people keep them as pets. Why do people say pigeons are clever? Because pigeons can take letters from one place to another. And they know the way home. We often see the picture of a pigeons with an olive branch(橄榄枝) in its mouth. We call them peace pigeons. They are the symbol of peace.

①皮肤②胃黏膜③神经细胞④蚯蚓⑤细胞内蛋白质等化合物⑥病毒⑦同一片草地上的所有山羊⑧一池塘中的所有鱼类⑨一片森林⑩一池塘中的所有生物

设max{x，y}表示x，y两个数中的最大值．例如“max{0，2}=2；max{8，12}=12；max{3，3}=3”，

请画出关于x的函数y=max{2x，x+2}的图象．