Which of the Following Assumptions Must Be True in Order $\bar { x } \pm z _ { \mathfrak { w } / 2 } \sigma / \sqrt { n }$

Multiple Choice

Which of the following assumptions must be true in order to use the formula $\bar { x } \pm z _ { \mathfrak { w } / 2 } \sigma / \sqrt { n }$ to find a confidence interval estimate of the population mean?

A) The population variance is known.
B) The population mean is known.
C) The population is normally distributed.
D) The confidence level is greater than 90%.