Answer:
d. highlighting key points.
Step-by-step explanation:
When reading a certain document, you can highlight the key points to determine the importance of the different ideas that the text expresses, so the most important ideas that the document speaks about are the ones that are going to end up higlighted, and those are the core of the documents, it´s what you should be left with. By doing this you can understand better the assignment and learn it better.