Many medical experts have suggested that excessive drinking of coffee is harmful to health. To verify the effect of excessive drinking of coffee on the heart, the researchers selected two groups of subjects. The first group of subjects drank 5 or more cups of coffee a day, and the second The subjects in the group never drank coffee. After a while, it was found that the proportion of subjects with heart disease in the first group was significantly higher than that in the second group. Therefore, the researchers concluded that excessive drinking of coffee increased heart disease. risks of. If one of the following is true, the above argument can be questioned most? ['Study finds that heart function is not affected in people who drink 2 cups of coffee daily.', 'During the study period, the daily exercise amount of the first group of subjects was significantly less than that of the second group of subjects.', 'In addition to affecting heart function, the caffeine contained in coffee is also prone to trigger anxiety.', 'Some of the subjects in the first group drink 10 cups of coffee daily.']