7.57 Multiple choice: CLT The central limit theorem implies

a. All variables have approximately bell-shaped data distributions if a random sample contains at least about 30 observations.

b. Population distributions are normal whenever the population size is large.

c. For sufficiently large random samples, the sampling distribution of x is approximately normal, regardless of the shape of the population distribution.

d. The sampling distribution of the sample mean looks more like the population distribution as the sample size increases.