Regarding statistical inference, which of the following statements is true?

a.Depending on how you treat a dataset (either as a sample or population), variance is calculated differently.

b.Population median does not exist, because the population size is infinite.

c.Everything else constant, a smaller sample size will make the sample mean a more precise estimate of population mean.

d.Sample size does not depend on the population size because population is the complete pool of random variables.