I think it would either be A or C
Structure in writing depends on what the objective - what the writer is trying to convey. If it is an argument, the structure will include a problem statement, supportive explanations and a conclusion. If it is a narrative, the structure can be subjective - the narration will go along with the observer throughout; or it can be chronological - a description based on time order. If it is simply writing something personal, then the structure can be flexible and free flowing.
B. That's when I realized the door had locked behind me.
Hole this helps! :)
