The correct answer is the fourth (D).
Although the first three alternatives may eventually contribute, none of them is a prerequisite for a successful marriage.
Living together before the wedding is meant to get to know each other better, but there is no indication that it will make the marriage last any longer. Likewise, religious and premarital counseling can help the couple, but without any guarantee. What makes the marriage successful is the couple's complicity, love and tolerance for the defects they both have.