Consider a hypothesis test of difference of means for two independent populations x1 and x2. What are two ways of expressing the null hypothesis?
a. H0: μ1 = μ2 or H0: μ1 + μ2 = 0
b. H0: μ1 < μ2 or H0: μ1 – μ2 < 0
c. H0: μ1 = μ2 or H0: μ1 – μ2 = 0
d. H0: μ1 > μ2 or H0: μ1 – μ2 > 0
