In Constructing a Confidence Interval for the Population Mean When $\bar { x } \pm t _ { n / 2 } \frac { s } { \sqrt { n } }$

Multiple Choice

In constructing a confidence interval for the population mean when the population variance is unknown, which of the following assumptions is required when using the following formula? $\bar { x } \pm t _ { n / 2 } \frac { s } { \sqrt { n } }$

A) The sample size is greater than 30.
B) The population variance is known.
C) The population is normal.
D) The sample is drawn from a positively skewed distribution.