The difference of sample means of two populations is 108.7, and the standard deviation of the difference in sample means is 32. which statement is true if we are testing the null hypothesis at the 68% confidence level? a) the difference of the two means is significant at the 68% confidence level, so the null hypothesis must be rejected. b) the difference of the two means is significant at the 68% confidence level, so the null hypothesis must be accepted. c) the difference of the two means is not significant at the 68% confidence level, so the null hypothesis must be rejected. d) the difference of the two means is not significant at the 68% confidence level, so the null hypothesis must be accepted.