The prefix "ecto" means?

• A. Out from
• B. In
• C. With
• D. Away

Answer: (A)

Ecto- denotes outside, exterior, or outer. This spatial sense is seen in terms like ectoplasm (the outer substance associated with cells or forms), ectoderm (the outermost tissue layer in early development), and ectoparasite (a parasite living on the outside of a host). Therefore the best way to express this prefix is "out from" or "outside." The other options don’t fit because they point to different relationships: "in" relates to inside (endo- or intra-), "with" implies accompaniment or together (co- or syn-), and "away" isn’t a standard directional meaning used with this root in medical terminology.