A sample mean, sample size, and population standard deviation are provided below. Use the one$-$mean z$-$test to perform the required hypothesis test at the $10\%$ significance level.

$\stackrel{}{x}=20,n=27,=4,H_0$:$=21,H_a$:$21$

The test statistic is $z=$

$($Round to two decimal places as needed.$)$

Identify the critical value$($s$).$ Select the correct choice below and fill in the answer box within your choice.

$($Round to three decimal places as needed.$)$

A$.$ The critical values are $+-z_{\frac{}{2}}=+-$

B$.$ The critical value is $-z_{}=$

C$.$ The critical value is $z_{}=$

the null hypothesis. The data sufficient evidence to conclude that the mean is