单项选择题
Given： What is the result？（）
A.Compilation fails. B.An exception is thrown at runtime. C.An instance of Forest is serialized. D.An instance of Forest and an instance of Tree are both serialized.
单项选择题 Given： What is the result？（）
单项选择题 Given： Which code fragment， inserted at line 23， allows the code to compile？（）
