The correct answer is Option B.
EXCEPT means exclusive of or excluding.
In the given sentence, the student found out that excluding him everyone had passed the exam.
Thus EXCEPT is the correct answer.
ACCEPT means to receive. This word does not go with the context of the sentence and hence is incorrect.
The remaining options are incorrect because:
Option A- NO CHANGE is incorrect because Option A is the correct answer.
Option C- INSTEAD OF is used in case of replacement.
Option D- WHILE refers to period of time.