Which prefix means against?

• A. Anti-
• B. Intra-
• C. -osis
• D. Against

Answer: (D)

A prefix that conveys opposition is anti-. This little piece in front of a root word signals that something is counter to or opposing the root’s action, as in antibiotic (against bacteria) or anti-inflammatory (opposing inflammation). Intra- means within, not against. The ending -osis is a suffix that turns a verb or root into a noun indicating a condition or process. The standalone word Against isn’t a prefix at all, so it doesn’t fit the question’s requirement. So the correct choice is the prefix anti-.