The answer is (d) other. Look carefully at the photograph below of the letters viewed through the rod, but with a finger added. Does looking at the finger through the rod help you to see why some of the letters appear upside down?
In fact, all of the letters are inverted - however, the red ones are symmetric about the horizontal centerline of the letters, so they look the same normal and upside-down.
Perhaps it is not necessary at this time to further debunk the other possibilities.
