Introduction:
Nazi Germany was a totalitarian state that relied on the support and compliance of the German population. While it is true that many ordinary Germans were passive onlookers and were scared to act or protest, it is not accurate to say that every German was a Nazi. This answer will delve into each option to explain why "D" is the correct choice.

Analysis:
a) Majority of Germans were passive onlookers:
- It is true that a significant portion of the German population did not actively resist or protest against the Nazi regime.
- This can be attributed to various factors, including fear of reprisal, propaganda, and the desire to avoid conflict or protect one's own interests.

b) They were scared to act, to differ, to protest:
- The atmosphere of fear and intimidation created by the Nazi regime made it difficult for ordinary Germans to express dissent or opposition.
- The Gestapo, the secret police, had extensive surveillance networks and employed brutal tactics to suppress any form of resistance.
- Fear of being arrested, imprisoned, or even killed deterred many from openly opposing the regime.

c) Majority genuinely believed Nazism would bring prosperity and well-being:
- It is true that a substantial number of Germans believed in the promises of the Nazi Party, particularly during the early years of Hitler's rule.
- The party's propaganda effectively portrayed Nazism as a solution to Germany's economic woes and a means of restoring national pride.
- Many Germans were desperate for stability and improvements in their living conditions, and thus, they embraced the Nazi ideology.

d) Every German was a Nazi:
- This statement is false and an oversimplification.
- While the Nazi Party gained significant support, particularly after Hitler's rise to power, not every German citizen was a member or supporter.
- Opposition groups did exist, such as the White Rose movement and the Confessing Church, who actively resisted Nazi policies.
- Additionally, there were individuals who may not have supported the Nazi Party but felt compelled to comply due to fear or social pressure.

Conclusion:
While it is true that the majority of Germans were passive onlookers, scared to act or protest, and believed in the promises of Nazism, it is not accurate to claim that every German was a Nazi. Opposition and resistance to the regime did exist, albeit in various forms and varying degrees of effectiveness. It is important to acknowledge the complexities and nuances of the experiences of ordinary people living under Nazi rule.