Answer - C - Piet Mondrian was not part of the Abstract Expressionism movement (otherwise known as the New York School).
Key Takeaway: The 1950s Abstract Expressionism movement, also known as the New York School, is generally considered to be the first American avant-garde art movement. Artists of this movement, like de Kooning, Pollock, and Nevelson saw themselves as taking a more active approach to abstract art, in which the artist's hand was more evident in the work. Abstract Expressionism sought to differentiate itself from artists like Piet Mondrian and Malevich.