In order to use a z statistic for testing a
hypothesis about a population mean,
Group of answer choices
(a) the sample data come from a simple random sample.
(b) the population has a Normal distribution; otherwise the
sample size should be at least 30.
(c) the value of the population standard deviation is known.
(a), (b), and (c)
(a) and (b)
(b) and (c)