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what is meant by an artist personal style and what role does it play on the historians efforts to identify artworks as representative of art movements?

An artist’s personal style just means it is an artist’s way of using the art elements and principles to reproduce what they see and to express their idea and feelings

In the visual arts, style is a "...distinctive manner which permits the grouping of works into related categories". or "...any distinctive, and therefore recognizable, way in which an act is performed or an artifact made or ought to be performed and made".

Iwould say 2: rhythm and repetition

The theme of social protest remained a consistent focus for jacob lawrence throughout his career. in the 1960s lawrence was inspired by news reports and photographs, including images of segregated lunch counter sit-ins and stories of the   freedom riders in the civil rights movement. from the 1970s onward, lawrence's work focused less explicitly on contemporary social issues.