Carl is clearly an incompetent detective. He has solved a smaller percentage of the cases assigned to him in the last 3 years -- only 1 out of 25 -- than any other detective on the police force. Which one of the following, if true, most seriously weakens the argument above? ['Before he became a detective, Carl was a neighborhood police officer and was highly respected by the residents of the neighborhood he patrolled.', 'Because the police chief regards Carl as the most capable detective, she assigns him only the most difficult cases, ones that others have failed to solve.', 'Carl was previously a detective in a police department in another city, and in the 4 years he spent there, he solved only 1 out of 30 crimes.', 'Many of the officers in the police department in which Carl serves were hired or promoted within the last 5 years.']