In my point of view you made the right choice by reviewing the question several times. At first, option A was confusing because it appears in the text, but it doesn't answer what is being asked. The key was to understand that the question asked what the teachers failed to do, and option C explains it correctly: they did not examine the causes of the events in depth. My tip for you: don't be guided only by what appears in the text; make sure the option answers exactly what is asked.