(2011·江西高考)It be the postman at the door.It's only six o'clock.
A. mustn't
B. can't
C. won't
D. needn't
网友回答
A. mustn't
(答案→)B. can't
C. won't
D. needn't
解析：选B 考查情态动词。句意：门口不可能是邮递员，(现在)才六点钟。 对现在的否定推测，由It's only six o'clock.分析可知应用can't(不可能)。mustn't“禁止”， won't“不会”，needn't“不必”，均不合句意。