Answer:
The correct answer would be bones.
X-rays are high energy electromagnetic waves which have an ability to penetrate most of the biological tissues.
In the X-ray machine, a beam of high energy X-rays is passed through the filters and subject and then fall on the detector or photographic film to produce X-ray.
Dense tissues like bone, teeth, tumors et cetera blocks or stops most of the X-ray particles from reaching the detector or photographic film.
It forms glowing pictures on the X-ray film or photographic film.
The denser the material the brighter the image will be formed on the photographic film.