Which combining form means cause?

• A. Chondr/o
• B. Eti/o
• C. Xanth/o
• D. Hydr/o

Answer: (B)

The main idea here is identifying a combining form that denotes origin or cause. Eti/o means cause, and it gives us words like etiology (the study of the causes of a disease) and etiologic (relating to cause). This is exactly what the question is asking for. The other roots point to something else: chondr/o is cartilage, xanth/o is yellow, and hydr/o is water or fluid. So eti/o is the appropriate choice because it conveys the notion of cause.