State the null hypothesis, Ho, and the alternative hypothesis, Ha, that would be used to test these claims:
a. The mean of the differences between the post-test and the pre-test scores is greater than 15.
b. The mean weight gain, after the change in diet for the laboratory animals, is at least 10 oz.
c. The mean weight loss experienced by people on a new diet plan was no less than 12 lb.
d. The mean difference in the home reassessments from the two town assessors was no more than $200.