"남자는 산을 오릅니다."
Translation:A man climbs a mountain.
I'm so confused by the choice of acceptable articles for these sentences, why is "the" accepted here and not in other similar sentences?
You are correct, but Duolingo is pretty consistent about using 남자아이 when they mean boy. So when on Duolingo, 남자 is man and 남자아이 is boy. But I agree - my understanding is that 남자 really just means "male".