import java.io.*；  public class Forest implements Serializable {  private Tree tree = new Tree（）；  public static void main（String [] args） {  Forest f= new Forest（）；  try {  FileOutputStream fs = new FileOutputStream（”Forest.ser”）；  ObjectOutputStream os = new ObjectOutputStream（fs）；  os.writeObject（f）； os.close（）；  } catch （Exception ex） { ex.printStackTrace（）； }  }  }  class Tree { }  What is the result？（） 

• A、 Compilation fails.
• B、 An exception is thrown at runtime.
• C、 An instance of Forest is serialized.
• D、 A instance of Forest and an instance of Tree are both serialized.