An auditor claims that the average annual salary of a project manager at a construction company exceeds $82,000. A random sample of 20 project managers had an average salary of $89,600 with a sample standard deviation of $12,700. Assume the salaries of the managers are normally distributed. You want to test the claim at the alpha = 0.01 significance level. If using the "critical value approach" for your hypothesis test, what will be your critical value(s)?
a. approximately 2.539
b. approximately 2.680
c. approximately 2.33
d. none of the above