问题
                    
The fog is so thick that the express way ____ have been closed. — You are right. I ____ have thought of that. Now we have to take another road.
                            A:can; should
B:may; can
C:should; must
D:must; should
                        
                        B:may; can
C:should; must
D:must; should
正确答案是:
                        