Riley, a child psychologist, claims that for all samples of size 40 from the population of infant boys and all samples of size 40 of newborn girls, the mean of the sampling distribution of the difference in sample means (boys minus girls) is 0.2 month. Is Riley correct? Yes, the mean is 8.1−7.9=0.2 month. A No, the mean is 0.8−0.7=0.1 month. B No, the mean is 8−8=0 months. C No, the mean is 8.1−0.8=7.3 months. D No, the mean is 7.9−0.7=7.2 months.