Answer: NSDAP was established in 1920. It was an expression of the disillusionment of one part of Germans after the First World War. It was that part that did not agree with Weimar regime. C is correct.
Explanation: NSDAP = national socialist party or nazi party. It was not founded by Hitler. At the very beginning socialism prevailed over nationalism. Hitler´s arrival to this party had a great effect: 1) he took advantage of above mentioned disillusionment in the German society, 2) he took advantage of ubiquity of anti-semitism. These two factors contributed significantly to his victory (1933 Hitler got legally to power - chanceller).