All the three roses are opaque and will have the same shadow. Regardless of the colour of the rose, the colour of the shadows will always be something darker than the colour of the wall. Thus, no rose could be distinguished from the other by looking at their shadows. So D is the correct answer.
Since the colour of the shadow doesn't depend on the colour of the object, you cannot distinguish the roses from each other as the colour of the shadow (black) will remain same for all the roses.