You are right about Constanca, but I dont know about Ljubljana because some people say that Slovenia belongs to Balkan and other say that it belongs to Central Europe.
The Balkans are most often defined by the area enclosed by the Sava, Soca and Danube rivers. This puts Ljubljana, Constanta and Trieste in the Balkans, and Novi Sad and Bucharest not.
This quiz is all kinds of wrong. The northern border of the balkans starts at Trieste and goes in a straight line to the south of Moldova and includes all land surrounded by sea below that point so you have missed Bucharest and Budapest
What about distance between south of Moldova and Black sea, is that area part of Balkan or not? Also if it was straight line Budapest still would not fit in. Recently I found out that borders of Balkan are rivers, Danube-Sava-Soča, and quiz will be updated accordingly.