创建Rodent（啮齿动物）：Mouse（老鼠）,Gerbil（沙鼠）,Hamster（大颊鼠）等的一个继承分级结构。在基础类中，提供适用于所有Rodent的方法，并在衍生类中覆盖它们，从而根据不同类型的Rodent采取不同的行动。创建一个Rodent数组，在其中填充不同类型的Rodent，然后调用自己的基础类方法，看看会有什么情况发生。要求把Rodent定义成为抽象类。-Create Rodent (rodent): Mouse (mice), Gerbil (sand rat), Hamster (hamster) and other hierarchical structure of a successor. In the base class, provide methods for all Rodent and cover them in the derived class, which according to different types of Rodent take different actions. Create a Rodent array, in which the filling of different types Rodent, then call their base class methods, see what happens. Requested that the definition of a Rodent abstract class.