A financial economist is studying married couples in which both spouses work

A financial economist is studying married couples in which both spouses work. He wants to compare the mean income earned by husbands with the mean income earned by their wives. Should he use independent sampling or dependent sampling, and why?

(a) Independent sampling. The two spouses are separate people with different jobs, so the husband's income doesn't depend on his wife's income.

(b) Independent sampling. How he selects the husband is independent of how he selects the wife.

(c) Dependent sampling. The husband's income depends to some degree on his wife's income.

(d) Dependent sampling. He needs to select couples for his sample, so whether a particular wife is included depends on whether her husband is included.