Explanation:

Break up (Phrasal Verb): End something 

From the given context, it is clear that we are talking about violent protests against the killing of school students by the militants and the phrasal verb used here is not correct contextually.  Rather, we should use the word erupted in this context since that will imply the desired meaning of the given statement that violent protests started. Other options are already out of context. 

It makes Option B the correct choice among the given options.