Missing options in the question:
a) a window
b) a mirror
c) a plaster wall
d) a steel beam
And missing figure (see attachment)
Solution:
The right answer is a) a window.
The light, in fact, when encountering a window is refracted inside the glass and it changes path. This happens twice, also when the light escapes from the other side of the window. instead, for all the other options the light is simply reflected back without crossing the object, therefore the correct answer is the window.
