REMOVE

1. sky
2. automobiles
3. roads
4. portraits
5. fields (land)
6. black-and-white film

WHAT

1. Visual Works (hierarchy n … (1)
2. artists (visual artists) (1)
3. branches (plant component … (1)

More 

WHEN

1. 1960 (1)
2. 1970 (1)
3. between 1960 - 1970 (1)