Wen kann man als Bürgerin/Bürger in Deutschland nicht direkt wählen?

Why this is the correct answer

Germany's President is not elected by a direct public vote but by the Bundesversammlung, a special assembly made up of all Bundestag members and an equal number of delegates chosen by state parliaments. Citizens vote directly for Bundestag members, state parliament members, and European Parliament members, but not for the President.