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 */ }