Suppose a Test Procedure About the Population Mean $\mu$ Is Performed, When the Population Is Normal and the Sample

Essay

Suppose a test procedure about the population mean $\mu$ is performed, when the population is normal and the sample size n is small, then if the alternative hypothesis is $H _ { \pm } : \mu \neq \mu _ { 0 } ,$
the rejection region for a level $\alpha$ test is either __________ or __________.