A researcher wants to prove that there is a difference in the average life spans between men and women in Japan. Let mu1 = average life span of Japanese women and mu2 = average life span of Japanese men. A random sample of 10 women showed an average lifespan of 83 years, with a sample standard deviation of 7 years. A random sample of 10 men showed an average lifespan of 77 years, with a sample standard deviation of 6.4 years. Assume that life spans are normally distributed and that the population variances are equal. What are the appropriate null and alternative hypotheses?
A. Ho: mu1 - mu2 = 0 and Ha: mu1 - mu2 > 0
B. Ho: mu1 - mu2 NE 0 and Ha: mu1 - mu2 = 0
C. Ho: mu1 - mu2 = 0 and Ha: mu1 - mu2 NE 0
D. Ho: mu1 - mu2 > 0 and Ha: mu1 - mu2 = 0