Hint: Trade was the first factor identified to unify Germany and subsequently unions were formed. The aim of this was to unify the Germans economically into a nation and also give rise to national sentiment in the people of the country.
Complete answer: In 1834 ,a customs Union , known as Zollverein was formed at the initiative of Prussia which was the predecessor of Germany.This union was joined by most of the German States. The aim of Zollverein was to bind the Germans economically into a nation to awaken and raise German people through a fusion of individual and provincial interest.Now let's see the options:
A) Diet: Diet was the parliament of Prussia and at that time it was an important factor in German unification but custom unions was the first step thus this option is incorrect. B) Military alliances: Military alliances were also very important in German unification but it was done through the efforts of otto von Bismarck which was much later than the Zollverein hence this is incorrect. C) Zollverein: delivery was a custom Union form to manage direct and economic policies within the territories. It also had a purpose of German unification hence this option is correct. D) Carbonari: Carbonari which means charcoal workers or makers in Italian was an informal secret revolutionary society active in Italy ,not Germany hence this is an incorrect option.
Hence the correct option is (C) Zollverein
Note: Zollverein included all German speaking States with exception of Austria. The economic integration which was initiated with Zollverein deepened with full political integration with the creation of German empire in 1871 by the efforts of Friedrich Von Motz and Otto Von Bismarck.