Question

What purpose does the illustration serve in the document?

Answer 1

I would need to see the document to better understand the question. It is most likely one of these two-- See explanations below.

C. If the illustration something that uses descriptive words, it "illustrating" the process so that the student can better understand it. This could also be a diagram or chart

D. If the illustration is a drawing or photograph, the answer is most likely D because it adds color and holds the reader's interest. It uses imagery