Which combining form means 'through, completely'?

• A. Circle
• B. Bladder, sac
• C. Down, from
• D. Through, completely

Answer: (D)

Understanding how combining forms express direction and extent is being tested here. A form that means “through, completely” signals thorough passage in medical terms. The prefix per- carries this sense, appearing in words like perforate (to bore through) and permeate (to pass through or through completely). So the option that states “through, completely” is the best match because it directly defines the meaning of that combining form. The other options point to unrelated ideas—circle describes a circular shape, bladder or sac points to cyst/o or sac/o, and down, from corresponds to a directional prefix such as de-—and do not convey the through/throughout meaning.