"I remember the Dnipro river."
Translation:Я пам'ятаю річку Дніпро.
Also, the Dnipro is really not a 'little river' (річка) - it is a 'BIG river' (РІКА). I never call the Dnipro a 'річка'. It's sacreligious!
this is not a brilliant set of alternatives. If, uniquely, you could only use the river-name alone (as well as the river-name plus річку = the river) in Ukrainian then the alternatives would be teaching you something. However, since you can also say just "the Dnieper" in English then arguably you should have just Дніпро in Ukrainian to translate that and річку Дніпро to translate "the river Dniepro" in English. Ok, they mean essentially the same but they are still both closer translations, respectively. That makes the answer (that both alternatives are equally valid) rather subjective and arguable and it's better if it's not.