Unlike English, French requires articles before almost all nouns. In this case, since the girls are eating an unspecified amount of rice, you need the partitive du. More here: https://www.duolingo.com/comment/3683850
Why "du" if it doesnt say that the girls are eating just "some rice". It says they are eating the rice, implies that they'll eat all of it...why use the article "du" if it means some and qualify me as wrong for it???? why? please someone explain.
"Du" is used to mean "of"=the girls are eating of the rice while "le" literally means the girls are eating the rice which is not what the question wanted and in french it is imperative you use articles almost everywhere