"ia" & "dia" , the differences :
https://forum.duolingo.com/comment/28585404

"Ia" and "Dia" means the same thing, "He/She/It". Indonesian doesn't distinguish between he, she, and it.

There are two things, though. "Ia" can only be used as a subject (like "he" but never "him"). "Ia mendorong dia" is "he/she/it pushes him/her/it" and it's a correct sentence, but "dia mendorong ia" is wrong. "Dia" can be shortened to "-nya" after verbs ("ia mendorongnya").

Another thing, "dia" tends to be used more often to refer to people, while "ia" is more often used to refer to things.

Synonims...