Which of the following is true? a, If the population distribution is normal, then regardless of the sample size n, the sampling distribution of the sample mean x" is also normal. b. The sampling distribution of the sample mean x" for a random sample of size n describes how observations tend to vary from subject to subject in a random sample of size n. C. Population distributions are normal whenever the population size is large. d. The standard deviation of the sample mean x" for a random sample size of n equals the population standard deviation o