French language Q&A Forum

Thanks for helping

 I am reading "Le Petit Prince" and noticed that sometimes, passé composé is used in the description (NOT the dialogue)  instead of passé simple. In simple sentences like "J'ai ainsi vécu seul" and "J'ai vu un petit bonhomme tout à fait extraordinaire". 

There are instances where you can (or *have to*???) use passé composé in literature? I can't find any pattern so can someone explain this to me?  

I don't understand the use of -t- in forming a phrase.  For example, why is "she accepted" written  "accepte-t-elle" instead of "elle a accepté"?

Could you briefly tell me when to use vous avez and vous étes since both mean "you are"?

or can we use either of them is any case?

I have a student who was taking an A0 test. She was asked how to say "Marie, you are a student." and was given the prompt 'Marie tu...'. She answered 'Marie tu es élève.' and Kwizbot told her that she was wrong, that it should be 'Marie tu es étudiante." Why would 'élève be incorrect? I was under the impression that they were interchangeable, so I need to understand the usage differences...

can anybody explain why one is used rather  than other please. in the question it was a mon pere and to finish sentence so i put a moi, but wrong and should be me.