What is a convention that Social Realist Ben Shahn used in his painting The Passion of Sacco and Vanzetti?

The Passion of Sacco and Vanzetti, painting by Ben Shahn, showing three men standing with flowers in hand near two coffins

Shahn made a strong statement about a historical event of the eighteenth century.

Shahn used flat shapes and sharp, angular forms to create abstract figures.

Shahn placed the most important figures in the center, representing them the most realistically.

Shahn employed a bold, Expressionist color palette to enhance the drama.