Testing:
$H O: u \geq 13.9$
$H 1: u< 13.9$
At $a=0.02$ the rejection region is

Step 1 ：We are given a null hypothesis \(H O: u \geq 13.9\) and an alternative hypothesis \(H 1: u<13.9\). The significance level is \(a=0.02\).

Step 2 ：We are asked to find the rejection region for a one-tailed hypothesis test. This is a left-tailed test because we are testing for a value that is less than a certain number.

Step 3 ：The rejection region would be any z-score that corresponds to a probability less than the significance level.

Step 4 ：To find the z-score that corresponds to a probability of 0.02, we can use the standard normal distribution table.

Step 5 ：The z-score that corresponds to a significance level of 0.02 is approximately -2.05. This means that any z-score less than -2.05 would fall in the rejection region.

Step 6 ：\(\boxed{\text{The rejection region is } z < -2.05}\)