Which prefix means 'Together' or 'mutual'?

• A. inter-
• B. tri-
• C. co-
• D. non-

Answer: (C)

Understanding how prefixes express relationships helps decode meanings quickly. The prefix co- conveys together, with, or mutual action—sharing in the same activity or purpose. That direct sense of joint effort is exactly what the prompt is asking for: a prefix that means doing something in common or with others. Think of words like cooperate, coauthor, or coordinate—they all hinge on acting together.

Inter- means between or among, which is a different nuance—it's about relationships across separate parts rather than shared, combined action. Tri- means three, and non- means not or absent. None of those convey the idea of joint action the way co- does. So the best fit for “Together” or “mutual” is co-.