"There are several open restaurants."
Translation:Det finns flera öppna restauranger.
I think it's just to have a distinction between when something has a certain trait and when something exists in a certain state. After all, "Det finns" literally means "it exists," so saying "Det finns flera öppna restauranger," is literally saying "Several open restaurants exist," or "There are several open restaurants." If you were saying something like "The restaurant is open," you would use "det är" because it's more for when something possesses a certain trait.
I think "många" is rather "many", not "several". "många restauranger" should not be accepted in the multiple choice answer.