A quality control specialist at a plate glass factory must estimate the mean clarity rating of a new batch of glass sheets being produced using a sample of 18 sheets of glass. The actual distribution of this batch is unknown, but preliminary investigations show that a normal approximation is reasonable. The specialist decides to use a t- distribution rather than a z-distribution because (A) The z-distribution is not appropriate because the sample size is too small.
(B) The sample size is large compared to the population size.
(C) The data comes from only one batch.
(D) The variability of the batch is unknown.
(E) The t-distribution results in a narrower confidence interval.