"Dragons appear in Vietnamese mythology."
Translation:Rồng xuất hiện trong thần thoại Việt Nam.
I will accept both singular and plural then. After all, it's the English sentence that affects this change. In the Vietnamese sentence, you rarely use classifier for this kind of generalization, thus it has to be plural (đàn ông mạnh hơn phụ nữ - men are stronger than women, chó thân thiện hơn mèo - dogs are friendlier than cats...)