Many people incorrectly think that all frogs are alike. In fact, there are hundreds of varieties of these ＿＿（21）＿＿ , which can live both on land and in water. The many types of frogs vary not only in sizes and colors but also in their abilities to survive in and ＿＿（22）＿＿ to different environments. For example, the green tree frog can change the color of its skin from tan to green to gray to yellow. This enables the frog to hide from its enemies wherever they are ＿＿（23）＿＿ . Another interesting example is the poison arrow frog, which is very dangerous. This frog's skin contains a poison powerful ＿＿（24）＿＿ to kill many larger animals that touch it. The frog also has a red stomach. When an enemy is near, the frog rolls ＿＿（25）＿＿ its back. The bright red color usually scares the enemies away. These two examples illustrate how different frogs can be.