Of the options given here, the best choice is to say that the Sacco and Vanzetti case was an example of nativism in the 1920s.  It might conceivably be seen as racial tension, but nativism is a better answer.

Sacco and Vanzetti were Italian immigrants.  They were also political radicals.  In the 1920s, people were very worried about both Italian immigrants and political radicals.  In the past three or four decades, many immigrants had come to the US from Italy.  They had also come from other countries in Southern Europe and from countries in Eastern Europe.  These were all places from which few immigrants had previously come.  “Native” Americans generally felt that these people were racially inferior because people in those days felt that there were different “races” of what we would now call white people. 

Because these new immigrants were from new countries, and because there were so many of them, they were very worrisome to many Americans.  Americans felt their country was being ruined by the immigrants.  This was particularly because they worried about the political attitudes of many of the immigrants and because they felt the immigrants did not want to assimilate and become “real” Americans.  This is a very nativist attitude.

Sacco and Vanzetti, their supporters claim, were targeted largely because they were Italian immigrants.  This is best seen as an example of nativism.