Why "En jente er et barn" was given me wrong (it should have been "ei jente") but here "en jente spiser ris" is correct?
Both "en" and "ei" are correct, but for listening exercises you need to enter the one that's actually being said.
Either, but be consistent. For Norwegians, it comes down to dialect.
I typed "the girl is eating rice", and it told me I was wrong, that is should be "the girl is eating rice" ... What?