Final answer:
The correct word to fill in the blank is option (A) 'regain,' which means to get something back, such as a divorced couple re-establishing their marriage.
Step-by-step explanation:
To regain something is to get it back. If a divorced couple remarries, they regain their marriage. The correct answer is A. regain.
To **regain** something means to obtain it again or to recover possession of it. In the context of the statement "If a divorced couple remarries, they **regain** their marriage," it implies that the couple is getting back together in marriage after a period of divorce. This term emphasizes the idea of restoring or reacquiring what was previously lost, in this case, their marital relationship.