public class X implements Runnable {  private int x；  private int y；  public static void main（String [] args） {  X that = new X（）；  （new Thread（ that ））.start（）；  （new Thread（ that ））.start（）；  }  public void run（） {  for （；；） {  synchronized （this） {  x++；  y++；  }  System.out.println（Thread.currentThread（）.getName（） +  “x = “ + x + “， y = “ + y）；  }  }  }   What is the result？（）  

• A、 Compilation fails.
• B、 The program prints pairs of values for x and y that might not always be the same on the same line （for example， “x = 2， y = 1”）.
• C、 The program prints pairs of values for x and y that are always the same on the same line （for example， “x = 1， y = 1”）.    In addition， each value appears only once （for example， “x = 1， y = 1” followed by “x = 2， y = 2”）.    The thread name at the start of the line shows that both threads are executing concurrently.
• D、 The program prints pairs of values for x and y that are always the same on the same line （for example， “x = 1， y = 1”）.     In addition， each value appears only once （for example， “x = 1， y = 1” followed by “x = 2， y = 2”）.    The thread name at the start of the line shows that only a single thread is actually executing.