Researchers performed group experiments on stroke survivors, and they asked one group of stroke survivors to exercise for 3 months outdoors under the supervision of researchers. The other group did not exercise, but received a therapeutic massage. After the conclusion, the researchers found that in the 6-minute test, the walking group walked farther than the massage group, and they could walk 17.6% more than the latter. The researchers believe that only moderately damaged stroke survivors More effective results can be obtained through simple and cheap exercises. Which of the following, if true, would most weaken the argument:. ['The average age of the A walking group was 72 years, and the average age of the massage group was 65 years.', 'Compared with the massage group, the improvement in physical fitness makes the stroke group survivors in the walking group have a higher quality of life.', 'Stroke survivors in the C-walking group also took related treatment drugs, and the massage group stopped taking related drugs.', 'Study proves better for stroke survivors with severe body damage.']