Which of the Following Is True

Which of the following is true?

A) The particular sampling distribution of the statistic in question is of fundamental importance in the determination of sample size. For example, the sampling distribution of the sample means is used when estimating a population mean.
B) It is impossible to specify both the degree of confidence and the degree of precision with a fixed size sample.
C) When determining the sample size necessary to estimate a population mean, it is helpful to know the population variance, for if one knows the population variance, he or she also knows the standard error of the mean up to a proportionality constant.
D) a and c
E) a, b, and c are all true