An experiment was conducted to test the hypothesis that exercise affects memory in the elderly. subjects aged 60 and older were recruited for the study. all of the subjects were presented with the same study list. then half of the subjects were asked to walk on a treadmill for 20 minutes, while the other half of the subjects were asked to complete sudoku puzzles for 20 minutes. then all subjects were given a recognition test for the iterns in the study list. the treadmill exercise group scored significantly lower on the recognition test than the sudoku puzzle group. which of the following cannot explain the results of this study? a. exercise decreases memory abilities b. more subjects with better memory were assigned to the sudoku group than the exercise group c. subjects in the exercise group paid less attention to the study list than subjects in the sudoku group d. exercise increases memory abilities