Which reader is most likely to find the photo in this document ?

a reader who is researching various types of energy efficiency
a reader who is experienced with do-it-yourself home repairs
a reader who installs windows for a living
a reader who is unfamiliar with the materials

Allusion and illusion. an allusion is an indirect reference, whereas an illusion is something that is unreal or incorrect. each of the nouns has a related verb form: allude “to refer indirectly to,” and illude (not a very common word), which may mean “to delude or deceive” or “to subject to an illusion.”