It's pretty logical once you know what to look for (Economist GMAT Tutor taught me this):

When you use "Which" it becomes some sort of an indirect clause (I may have the wording wrong) that essentially means that when you use "Which" it is often additional information whereas "That" provides necessary information.
In this case, the information is necessary to make sense of what is being said after the last comma. Rule out options C, D, E.
Between A and B, B implies that the student had been suspended once before as well, so that is ruled out. A!!