The t-distribution is used in constructing a confidence interval for a population mean in which of the following cases?
A) The population is normally distributed and the population standard deviation is estimated from a small random sample.
B) The random sample is small and population variance is unknown.
C) The sample size is small, the population is normal, and the population standard deviation is known.
D) The population is normally distributed, the sample size is 16, and the variance of the sample mean is unknown.
E) Both A and D