Which prefix means 'Within'?

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

Answer: (B)

Within is conveyed by the prefix intra-. It comes from Latin and means inside or within a structure. In medical terms, intra- shows up in words like intracranial (inside the skull), intramuscular (within muscle), and intravenous (inside a vein). The other options point outward rather than inward: extra- means outside or beyond, while ecto- and exo- also refer to outside or external. So intra- is the best match for “within.”