OE:
Research indicates that there is a connection between being married and being happy and healthy. Media commentators have concluded that marriage causes happiness and health. However, one could reasonably conclude from the research that the cause and effect are the reverse: being happy and healthy makes a person more likely to get married.

(A) The research compared married people to unmarried people. Neither the researchers nor the media commentators made any distinction between newlyweds and those who had been married a long time, so this assumption is not necessary.

(B) The type of wedding is outside the scope of this argument. The research compared married people to unmarried people, but made no distinction based upon the type of wedding. Thus, this assumption is unnecessary.

(C) At first, this statement may seem necessary—after all, if the commentators conclude that marriage causes happiness, a lack of depression in married people would certainly support that conclusion. However, the statement is too extreme. One depressed married person does not invalidate the research indicating that, on average, married people are healthier and happier than non-married people.

(D) CORRECT. This statement eliminates the alternative interpretation of the research findings—that being happy and healthy makes a person more likely to get married.

(E) The research compared married people to unmarried people. Neither the researchers nor the media commentators made any distinction between harmonious marriages and combative marriages, so this assumption is not necessary.