Using our context clues, the theory of a central fire most likely means:
that the center of the earth was made of fire
that a fire must exist in the center of all thing
that if one is going to build a fire, it should be centrally located
that fire explodes eventually

b is the answer to your question.

hmm, sadly there is no dialogue. there is no place in the story where he is talking to anyone. it's more of just describing what he eats and where he sleeps. you have to become anne frank, give details of where you are, what other folks look like, how the environment is. have a little bit of dialogue tell of what people are specifically saying. anne frank talked about her entire household including the people, the objects, the lighting, the food they ate, and even the smell in the air. there has to be more to your diary entries, the whole story in its current state is only about peter van daan, the food, the sounds, and where he sleeps. also he seems to be writing only once a year yet more than that happened from day to day. for a friend, i can you write it out, if you want.