Twenty years ago, the average term of employment for the Postal Service was 9 years. A sample of 100 current current postal employees found that the average time these employees had worked for the postal service was X (mean) = 7 years with s = 2 years. The researchers want to test whether the mean term of employment has changed from what it was twenty years ago. What hypotheses are appropriate for this test?
A. H0: Mu = 7 and H1: Mu not equal to 7
B. H0: X (mean) = 7 and H1: X (mean) not equal to 7
C. H0: X (mean) = 9 and H1: X (mean) not equal to 9
D. H0: Mu = 9 and H1: Mu not equal to 9