A.Compilation fails.
B.An exception is thrown at runtime.
C.The code executes normally and prints "sleep".
D.The code executes normally， but nothing is printed.

A.The code will deadlock.
B.The code may run with no output.
C.An exception is thrown at runtime.
D.The code may run with output "0 6".
E.The code may run with output "2 0 6 4".
F.The code may run with output "0 2 4 6".