Im pretty sure "거리에 용 두마리가 있어요" should also be correct
I second this.
I typed 용 두 마리가 길에 있어요. It was marked wrong. 길 means road.
Hover shows only 길, but the choices in the little box had 거리. Hover and the choices need to match. I will report that my answer should also be accepted.
What is 마리가 in this sentence?
It is the counting word for animals. The sentence means There are dragons (2 animals) on the road.