Do One of the Following, as Appropriate: (A) Find the Critical

Do one of the following, as appropriate: (a) Find the critical value $z _ { \alpha / 2 }$ , (b) find the critical value $t _ { \alpha / 2 }$ , (c) state that neither the normal nor the $t$ distribution applies.
$90 \%$ confidence interval for $\mu ; n = 9 ; \sigma = 4.2$ ; population appears to be very skewed.

A) $z _ { \alpha / 2 } = 2.896$
B) $z _ { \alpha / 2 } = 2.365$
C) $z _ { \alpha / 2 } = 2.306$
D) Neither the normal nor the $t$ distribution applies.