REMOVE

1. gray
2. black
3. workers
4. 1936
5. 1938

WHAT

1. Visual Works (hierarchy n … (1)
2. banks (landforms) (1)
3. black-and-white film (1)
4. bushes (1)
5. freight cars (1)

More 

WHO

1. Clyfford Still; Still, Cl … (1)
2. Still, Clyfford (1)

WHEN

1. 1920 (1)
2. 1940 (1)
3. between 1920 - 1940 (1)