is the pronounciation different between "ντ" and just "τ" ?
Yes, "ντ" is closer to the sound of "d" or "nd".
but i can write both like here?
Only for the word "tomato", which is called both ντομάτα and τομάτα.
No, the correct is ντοματα only
Duolingo is not correct here too , because it says that τοματα and ντοματα is correct ! Guys, the correct word here is ντοματα #ONLY!!
(The word τοματα, means NOTHING)