Questions & Answers about Moja sestra živi u gradu, ali moj brat živi u kući.
Because moj / moja / moje must agree with the gender of the noun.
- sestra is a feminine noun, so you use moja
- brat is a masculine noun, so you use moj
This is the same possessive adjective, just in different forms.
A few basic forms are:
- moj brat = my brother
- moja sestra = my sister
- moje dete = my child
So the ending changes to match the noun.
Serbian normally does not use articles like English the and a/an.
So:
- sestra can mean sister, a sister, or the sister
- brat can mean brother, a brother, or the brother
- grad can mean city, a city, or the city
The exact meaning depends on context. This is very normal in Serbian, so learners have to get used to understanding definiteness without articles.