Which of the following involve independent samples?

a. To test the effectiveness of the Atkins diet, 36 randomly selected subjects are weighed before the diet and six months after treatment with the diet. The two samples consist of the before/after weights.

b. To determine whether smoking affects memory, 50 randomly selected smokers are given a test of word recall and 50 randomly selected nonsmokers are given the same test. Sample data consist of the scores from the two groups.

c. IQ scores are obtained from a random sample of 75 wives and IQ scores are obtained from their husbands.

d. Annual incomes are obtained from a random sample of 1200 residents of Alaska and from another random sample of 1200 residents of Hawaii.

e. Scores from a standard test of mathematical reasoning are obtained from a random sample of statistics students and another random sample of sociology students.