Some twentieth-century art is great art. ███ █████ ███ ████████ ████████ ██████ ███ ███ ███ ████ ██ ███ ███████████ ██████ ██ █████ ████
The stimulus can be diagrammed as follows:
Some 20th century art involves original ideas.
Some 20th century art is influential.
Some art that involves original ideas is influential.
If art is great, then it is original and influential.
Each of the following statements ███████ █████████ ████ ███ ███ ██ ██████████ █████ ███████
Some influential art ████████ ████████ ██████
This must be true. As shown in the diagram, we can infer that some influential art involves original ideas.
Some twentieth-century art ████████ ████████ ██████
This must be true. As shown in the diagram, we can infer that some twentieth century art involves original ideas.
Only art that ████████ ████████ █████ ██ ████████████
This could be false. (C) can be diagrammed to say influential→ original. This is not a conditional claim given in the stimulus.

Only art that ██ ███████████ ███ ████████ ████████ █████ ██ █████ ████
This must be true. As shown in the diagram, all great art is influential and original.
Some twentieth-century art ██ ███████████ ███ ████████ ████████ ██████
This must be true. As shown in the diagram, there must be at least some overlap between art involving original ideas and influential art.