Which prefix indicates lack of or absence of?

• A. Peri-
• B. Endo-
• C. A-/An-
• D. Exo-

Answer: (C)

Think about how medical terms convey negation. A prefix that means without or lacking attaches to a root to express the absence of that feature. The form a-/an- does this, written as a- before consonants and an- before vowels in practice. You can see it in words like anesthesia (without sensation), anemia (without enough blood), and anhydrous (without water).

The other prefixes describe where something is or how it relates to another part of the body—peri- means around, endo- means inside, exo- means outside—which is about location, not absence. Because the question is asking which prefix signals lack or absence, a-/an- is the best fit.