SCJP 6.0認證教戰手冊考題.228---锁的问题

Which three will compile and run without exception? (Choose three.)        
                                                                           
A.    private synchronized Object o;                                       
                                                                           
B.    void go(){                                                           
                                                                           
       synchronized(){/* code here */}                                     
                                                                           
C.    public synchronized void go(){/* code here */}                       
                                                                           
D.    private synchronized(this) void go(){/* code here */}                
                                                                           
E.    void go(){                                                           
                                                                                                                                                                                                                                                   
      synchronized(Object.class){/* code here */}                          
                                                                           
F.    void go(){                                                           
                                                                           
      Object o = new Object();                                             
                                                                           
      synchronized(o){/* code here */}                                     
                                                                           
答案：CEF        我觉得答案错了，F无法保证加锁，因为锁对象是临时变量o，那么每个线程进入go的时候都可以可以获得一个不同的o，从而可以加上锁，我下面的代码也验证了这点，还有对于D，是否正确呢？public class Threads4 {
    Object obj = new Object();
    public static void main(String[] args) throws Exception {
        class Mythread implements Runnable {
            Threads4 t4;            Mythread(Threads4 t4) {
                this.t4 = t4;
            }            public void run() {
//                System.out.println("start " + Thread.currentThread().getId());
                try {
                    t4.go();
                } catch (Exception e) {
                    e.printStackTrace();
                }                System.out.println("end " + Thread.currentThread().getId());
            }
        }
        Threads4 t4 = new Threads4();        Thread t1 = new Thread(new Mythread(t4));
        Thread t2 = new Thread(new Mythread(t4));
        t1.start();
//        Thread.sleep(2000);
        t2.start();
    }    public  void go() {
        synchronized (obj) {
            double d;
            System.out.println(Thread.currentThread().getId()+" in loop");
            for (int i = 0; i < 100; i++)
//                for (int j = 0; j < 1000000; j++)
//                    for (int k = 0; k < 1000000; k++)
                System.out.println(Thread.currentThread());           System.out.println(Thread.currentThread().getId()+" out of loop"); 
        }
    }}