A proposed null hypothesis states that there is no difference in the population mean heights of males of two neighboring towns. The sample mean difference is found to be 10 cm, and the standard deviation of the difference of the sample means is 6 cm. Which statement is true? A. The null hypothesis must be rejected if we choose the 68% confidence level. B. The null hypothesis must be rejected if we choose the 95% confidence level. C. The null hypothesis must be rejected if we choose the 99.7% confidence level. D. The null hypothesis must be rejected if we choose the 100% confidence leve.