What root corresponds to 'X-ray'?

• A. Oste/o
• B. Rad/i
• C. Endarterial
• D. Radi/o

Answer: (D)

Radi/o is the root that signals radiation or X-rays in medical terms. That's why it fits X-ray concepts—the words radiograph, radiology, radiopaque all revolve around using or studying X-ray imaging. The combining form radi/o shows up specifically in terms dealing with radiation and imaging, so it’s the correct root for X-ray.

Oste/o means bone, which isn’t about imaging with X-rays. Endarterial refers to the inner lining of an artery, again not related to X-ray terminology. Rad/i relates to rays in other contexts or to the radius bone, so it doesn’t convey the X-ray meaning the way radi/o does.