Answer:
The correct answer to the question: Why might a student assemble books and magazines that are all on the same subjects, is: that the student is doing so most probably to categorize them and organize them into that category. This also will help in cataloguing different sources that deal with the same subject.
Step-by-step explanation:
The process of assembling books, and other sources such as magazines, means that a person is grouping them, and organizing them by subject, as is stated in the question itself, most likely to categorize these resources. This will also help with cataloguing. If there will later on be use of this materials, then the student will not need to look everywhere for resources; he/she will have them already organized and sorted by topic.