A fast way to solve paragraph ordering questions like this one is to find the phrases that cannot stand on their own and work out what they must be pointing back to, rather than reading every possible order in full.
Two phrases stand out here. Sentence "a" opens with "one of them," which only makes sense if some group of people has already been named. Sentence "d" ends by mentioning "the consequences of the illegal act," which only makes sense if a rule or warning has already been introduced, so that ignoring it counts as "the illegal act." Both of these point back to sentence "b," the guide's presentation on plagiarism to his students, so "b" has to come first, and it introduces the "students" that "one of them" in "a" refers to.
Once "b" is fixed as the opening sentence, "d" naturally follows it, since it directly continues the idea of students facing consequences after being warned. Sentence "a" comes next, narrowing "a few students" down to the specific "one of them" who actually copied text. Sentence "c," the expulsion order, closes the paragraph as the outcome of that act.
This gives the order b, d, a, c, with every reference word resolved by the sentence right before it.
So, the correct answer is bdac.
Another way to solve this type of question is to ignore full sentence meaning at first and track only the small linking signals inside each sentence, pronouns, time words, and phrases that point backward, then use just those signals to chain the sentences together.
Chaining only the pronouns and connective phrases, without relying on full sentence meaning, still lands on the same sequence.
So, the correct answer is bdac.