Final answer:
The conclusion that marriage improves health and happiness rests on the assumption that those with depression or health issues are equally likely to marry as others, ensuring the sample isn't biased.
Step-by-step explanation:
The conclusion of media commentators that being married is good for one’s health and attitude depends on several assumptions. However, the correct assumption in this context is most likely (D) Single people with depression or health problems are just as likely to get married as are other single people. This assumption must be true for the conclusion to hold; otherwise, it could simply be the case that healthier and happier individuals are more likely to get married, rather than marriage causing these positive outcomes.
It's important to note that while marriage has been associated with benefits such as well-being and reduced competition among individuals, the effects of marriage on happiness and health are varied and can depend on the quality of the marriage. Additionally, cultural and personal views on marriage can greatly influence individual experiences and choices surrounding marriage.