Which combining form means 'two, twice, double'?

• A. Circle
• B. Bladder, sac
• C. Two, twice, double
• D. Through, completely

Answer: (C)

Understanding numeric meaning in medical terms is key here. When a combining form expresses quantity, it signals that something is twofold or paired. The phrase “two, twice, double” directly describes that numeric sense the combining form carries. That exact meaning is what the correct option conveys, so it’s the best match. Other choices point to different concepts (circle, bladder/sac, or through/completely) and don’t describe a numeric or dual meaning, which is why they aren’t the right fit. In practice, you’ll see numeric prefixes like di- or bi- used to indicate two, and diplo- to indicate double, all built from the same idea of twofold quantity.