A doctor who has long been engaged in research on drunkenness and alcoholism found that, in general, drunks have a much higher tendency to violence than non-drinkers or moderate drinkers, and based on this, the doctor concluded that people with a tendency to violence are more likely to get drunk. Which of the following severely weakened the doctor's conclusion? ['Some people who have never drunk alcohol also have a strong tendency to violence.', 'When drinking and drinking addiction, people tend to act out of control and violent.', 'Violence is often used to vent grievances when people are drunk.', 'When a person is very drunk, he can no longer control his behavior, even if violence occurs, it will not cause serious consequences.']