Which of the Following Critical Values Is Appropriate for a $\sigma = 27$

Multiple Choice

Which of the following critical values is appropriate for a 98% confidence level where n=7 ; $\sigma = 27$ and the population appears to be normally distributed.

A) $z _ { \alpha / 2 } = 2.33$
B) $z _ { \alpha / 2 } = 2.05$
C) $t _ { \alpha / 2 } = 1.96$
D) $t _ { \alpha / 2 } = 2.575$