Colleen replicates an X-ray machine by covering an open shoebox with a screen and positioning a square cardboard piece in the center. She uses sand to simulate X-ray radiation, sprinkling it over the screen. Upon removing the screen, she observes an outline of the square cardboard. What does the cardboard symbolize in her simulation? (1 point)
O the person being scanned with X-rays
O the bones that look white in an X-ray
O the veins that look white in an X-ray
O the areas that remain black on the X-ray