Answer:
The correct answer is monogamy.
Step-by-step explanation:
Monogamy is the term which refers to a relationship between only one woman and only one man, or only two men, or only two women. The prefix monos means one/single, whereas the root gamos means marriage. Therefore, the meaning of monogamy is clear - only two people are involved in the relationship. It is the most common type of relationships and marriages, although it is certainly not the only one.
When a relationship consists of more than two people, then it is called polygamy.