exo- means which of the following?

• A. Inward
• B. Within
• C. Outward
• D. Across

Answer: (C)

Exo- is a prefix that signals location relative to the body or a reference point, specifically that something is outside or outward. When you attach exo- to a word, you’re describing something on the outside or away from the center. For example, exoskeleton encases the body from the outside; exocrine glands release substances to the outside of a body cavity or into ducts; an exogenous nutrient comes from outside the body. The opposite prefix endo- means inside, as in endoscope or endogenous. Since exo- conveys outward, the meaning here is outward. Other options describe inward or within, which would use prefixes like endo- or intra-, or across, which would use trans-.