REMOVE

1. wheat
2. farms
3. machinery
4. rock
5. farming

WHAT

1. Visual Works (hierarchy n … (1)
2. black-and-white film (1)
3. combines (1)
4. farmers (1)

More 

WHERE

1. Bow Island, Alberta, Cana … (1)

WHO

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

WHEN

1. 1931 (1)
2. ca. 1931 (1)