在一座大厦的第19层,牙医亨利开了一间诊所。一天下午,他正为玛丽小姐治牙,他们身后的门悄悄地开了条缝,“啪,啪”两声枪响,玛丽小姐倒在椅子里,饮弹毙命。一位电梯工在案发前不久,曾送一个神色紧张的男子上19层。根据他的描述,警方断定是假释犯约翰。约翰被传唤到警署,他说从未听说过亨利医生,在案发那天都在寓所睡觉。警官追问:“电梯工却说在案发前不久送过一个相貌特征与你相同的人士上19层,这您又作何解释?” On the 19th floor of a building, dentist Henry opened a clinic. One afternoon he was treating Miss Mary and the door behind them quietly slit, “snapped,” shot twice, and Miss Mary fell in a chair, shot dead. Shortly before the incident, an elevator worker sent a man with a nervous look on the 19th floor. According to his description, the police concluded that it was a parole of John. John was summoned to the police station and said he had never heard of Dr. Henry and was sleeping in his apartment on the day of the crime. The police officer asks: “The elevator worker said that just before the incident, there was 19 floor on the same person who looks like you. How do you explain this?” "