Hi! I hope that I answer your question to what you need.
To answer this question read the paragraph very carefully. First also review your answers, it will give you better insight on what the question is really asking for. Look at the main events in this reading. This reading is showing the emotions between Marina and Sharon. It shows how offended Marina is, but also Sharon's guilt and apologetic behavior. They have yet to find the cake culprit so it is NOT D. The reading does not say that the Marina was lying so it is NOT A OR B. Gathered from the evidence and reading, the best answer is C: to show how the events of the disappearing cake upset Marina and Sharon.
Please let me know if you need any clarification. I'm always happy to answer your questions.