Why дівчини is wrong?!
I think this should be 'what are THE girls doing at the Post Office?' Omitting the 'the' sounds odd - as if all girls are doing something at the Post Office!
"What are girls doing at the post office?" - This is about girls in general. Girls aren't allowed in the post office. Why are they here?
"What are the girls doing at the post office?" - This is seems to be what is intended.
Why is дівчинки wrong?
Can someone please explain the difference between у or в and на?
I'm afraid it just has to be remembered. На пошті, на вокзалі, на роботі, на вулиці, на площі, but у школі, в кімнаті, в будинку, в садку, в парку, в автобусі, в університеті.
Ok, thanks for the reply, I guess I am going to learn all of them one by one.
I can't finish the lesson! Right sentence doesn't work!