Now pronounce a sentence with the same obviousness intonation. Imagine that you are speaking with a friend. You are talking about a common friend, Maria. You tell Joan that Maria is pregnant. He asks you who is the father. You think that he should know this information because everybody knows that the father is Jordi, his partner, and you tell him "De'n Jordi!". After saying it, listen how it is pronounced.
Imagine that you are talking with your brother. He asks you when your birthday is. You know that he should know it because you are brothers, you tell him "El sis de novembre!". After saying it, listen how it is pronounced.
Now imagine that you are talking to your partner. H/she asks what did your brother studied. You know that H/she should know it because h/she even has lent him books sometimes. You tell him/her that your brother studied "Matemàtiques!". After saying it, listen how it is pronounced.