Which prefix expresses 'Within'?

• A. Ecto-
• B. Exo-
• C. Con-
• D. Intra-

Answer: (D)

Within is conveyed by the prefix intra-. It comes from Latin intra meaning inside, so it’s used to indicate something located inside a structure, as in intramuscular (within muscle), intracranial (within the skull), or intravenous (within a vein). Other prefixes here describe different spatial relations: ecto- and exo- mean outside or outer, and con- generally means with or together, not inside. So intra- is the best fit for indicating “within.”