Final answer:
Research indicates that couples who are committed to each other are typically committed to the institution of marriage as well, while equal power in relationships can actually foster commitment, contrary to option B. Commitment also encompasses various factors, not just a singular expectation or action.
Step-by-step explanation:
According to research regarding people's commitment to marriage, option A - couples who were highly committed to each other are usually also strongly committed to the institution of marriage itself - is the most accurate. Research has shown that there is a strong correlation between a couple's commitment to each other and their commitment to the institution of marriage. This makes sense considering the role marriage plays in society and the expectations that come with it.
Option B is not supported by research as equal power in relationships can actually contribute to a balanced and healthy relationship, which may encourage commitment. Moreover, commitment is not a singular expectation or action, as stated in option C; it involves a myriad of behaviors, decisions, and emotional investments that contribute to the stability of the relationship and the institution of marriage.