c Does 30 minutes of aerobic exercise each day provide significant improvement in mental performance To investigate this issue a researcher conducted a study with 150 adult subjects who performed aerobic exercise each day for a period of six months At the end of the study 200 variables related to the mental performance of the subjects were measured on each subject and the means compared to known means for these variables in the population of all adults Nine of these variables were significantly better in the sense of statistical significance at the a 0 05 level for the group that performed 30 minutes of aerobic exercise each day as compared to the population as a whole and one variable was significantly better at the 0 01 level for the group that performed 30 minutes of aerobic exercise each day as compared to the population as a whole It would be correct to conclude O A that there is very good statistical evidence that 30 minutes of aerobic exercise each day provides improvement for the variable that was significant at the a 0 01 level We should be somewhat cautious about making claims for the variables that were significant at the 0 05 level O B that there is very good statistical evidence that 30 minutes of aerobic exercise each day provides some improvement in mental performance C that these results would have provided very good statistical evidence that 30 minutes of aerobic exercise each day provides some improvement in mental performance if the number of subjects had been larger It is premature to draw statistical conclusions from studies in which the number of subjects is less than the number of variables measured D none of the above