The correct answer is answer A ("Indicate relationships between ideas").
The main thing we're trying to accomplish when utilizing transitional phrases or words, is to keep the text flowing smoothly. This serves to guide the reader along from one idea to the next in an orderly fashion that preserves clarity. Without transitional phrases or words, many times an interpretative essay will result in a convuluted mess of disjointed thoughts, which will surely be a problem for anyone reading it afterwards.
Hope this helps!