Final answer:
The most change for a couple typically occurs during parenthood, where new responsibilities and lifestyle adjustments are necessary as they transition from partners to parents.
Step-by-step explanation:
The stage of the life cycle that typically presents the most change for a couple is parenthood (option b). Parenthood is a significant transition period in the lives of a couple, as it involves a major shift in responsibilities, lifestyles, and relationships. Early adulthood is a period of establishing one's career path, forming intimate relationships, and often involves completing education and starting a family. However, it is during parenthood when the couple must adapt to caring for and raising children, which presents new challenges and requires significant adjustments in daily life and long-term planning. This stage is characteristically marked by a dramatic increase in responsibility and changes in social roles as individuals transition from partners or significant others to parents. These changes can have profound effects on a couple's life, including how they manage their time, finances, and social interactions, as well as their identities and emotional states.