Questions & Answers about Mój ojciec wraca z pracy późno.
Because mój has to agree with ojciec in gender, number, and case.
- ojciec is masculine singular
- the sentence uses the nominative case, because ojciec is the subject
So the correct form is:
- mój ojciec = my father
Compare:
- moja matka = my mother
- moje dziecko = my child
So mój / moja / moje work like gender-matching forms of my.
Ojciec is in the nominative case because it is the subject of the sentence — the person doing the action.
In this sentence:
- Mój ojciec = the subject
- wraca = the verb
- z pracy = from work
- późno = late
You may see other forms of ojciec in different sentences, for example:
- Widzę ojca = I see my father
- Mówię o ojcu = I’m talking about my father
But here, since he is the subject, Polish uses ojciec.