REMOVE

1. towers (building divisions)
2. trees
3. campuses
4. doors

WHAT

1. Visual Works (hierarchy n … (1)
2. black-and-white film (1)
3. buildings (structures) (1)
4. colleges (buildings) (1)

More 

WHERE

1. San Francisco, California (1)

WHO

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

WHEN

1. 1946 (1)
2. 1950 (1)
3. between 1946 - 1950 (1)