Final answer:
Couples who live together without being married are engaging in cohabitation, which is becoming more common as societal attitudes shift. The correct option is D.
Step-by-step explanation:
When couples share a home and a bed without being legally married, they are practicing cohabitation. This lifestyle choice has become more prevalent over the years, with the U.S. Census Bureau reporting an increase in cohabitation rates.
Many couples view living together as a way to spend more time together, save on living costs, or as a "trial run" for marriage. As societal perspectives continue to evolve, cohabitation is now seen as an acceptable step towards marriage or a stable alternative to it, with many cohabiting couples eventually transitioning into marriage.