"You have a father?"
Translation:Du hast einen Vater?
I thought it was 'hast du einen Vater?' the verb doesn't go first in questions?
The finite verb does go to initial position but sometimes Duolingo wants the word order of the original sentence. The "normal" English question would be "Do you have a father?" Since the "you" is in initial position, they might want "Du" in initial position as well.
Akkusative! It is useful to ask a question: Wen hast du? (Who do you have? Ich habe einen Vater (I have a father). This doesn't change when the sentences changes to a question: "Hast du einen Vater?" Hope this helps.
but why accusative? if it were to form the sentence without question, i mean "ich habe ein Vater" , it would had been without accusative. Or it would be accusative?! O.O
It would be. In English you would also say "I have him" and not "I have he". "haben" + Akk. "Ich habe einen Vater."
You are right, duolingo apparently doesn't care much about formal address in German, although if you go to Germany you WILL be addressed formally by EVERYONE who you never met before..!
I Ich habe You informal Du hast he, she, it er, sie, es hat we wir haben they, she ihr hat you formal Sie haben