Which Critical Value Is Appropriate for a 99% Confidence Level $\sigma$

Multiple Choice

Which critical value is appropriate for a 99% confidence level where n = 17; $\sigma$ is unknown and the population appears to be normally distributed?

A) $t _ { \alpha / 2 } = 2.921$
B) $z _ { \alpha / 2 } = 2.583$
C) $z _ { \alpha / 2 } = 2.567$
D) $t _ { \alpha / 2 } = 2.898$