Answer:
D. It helps the reader connect the strucutre with the purpous of each section.
Explanation:
D is the correct answer because subheadings provide the reader with a little bit of context for what they are about to read. Using process of elimination the answer is not B because the reader is not writing a summary. You are answering the question assuming that the person reading the subheadings have no additional activities that go along with their readings.