Introduction:
The question asks about the individual who topped the list of undesirables among the given options: Blacks, Jews, Gypsies, and Nordic Aryans. The correct answer is option 'B,' which refers to Jews.

Explanation:
Jews:
Jews have historically faced discrimination and persecution in various parts of the world. Anti-Semitism, which refers to prejudice against Jews, has been prevalent throughout history, leading to their exclusion and mistreatment.

Blacks:
Black individuals have also faced racial discrimination and slavery throughout history. However, in the context of the given options, they were not specifically targeted as the top undesirables.

Gypsies:
Gypsies, also referred to as Roma, have faced marginalization and discrimination in different societies. They have often been subjected to prejudice, exclusion, and stigmatization. However, in the context of the given options, they were not specifically identified as the top undesirables.

Nordic Aryans:
The term "Nordic Aryans" refers to a concept associated with Nazi ideology during World War II. The Nazis believed in the superiority of the Aryan race, particularly those of Nordic descent. While this ideology promoted the idea of racial purity and superiority, it does not specifically address the question of the top undesirables.

Conclusion:
Among the given options, Jews topped the list of undesirables. Throughout history, Jews have faced discrimination, persecution, and exclusion in various societies. Understanding this historical context is crucial to addressing and combating anti-Semitism and promoting equality and tolerance.