Answer choice B could be easy to select. I had it as a contender for a bit before landing on C. Here is why B is wrong and C is right:
Side note: If you are ever stuck between two or more answer choices something that has helped the light bulb turn on for me has been to re-read the question again to remind yourself what exactly it's asking.
So we are asked what "Bearden's innovative painting techniques illustrate"
(B) This is a deceitful answer choice because it's found in the same paragraph of the passage where they discuss Bearden's painting technique. However, this answer choice does not so much reflect what his painting technique was trying to illustrate but rather a belief that Bearden holds about how an artist should approach their craft. It's actually a poor answer choice even on that account though because there is no "desire to instruct" that can be inferred from this paragraph, but rather a belief Bearden holds to be true about how an artist should approach their craft.
(C) This is it. The direct support is found in lines 8-14 where the author starts out talking about Bearden's unique style, and then goes on to talk about how this suggested "some of the ways in which commonplace subjects could be forced to undergo a metamorphosis . . ." The word suggested as it is used in this passage is synonymous with illustrates. We've got a winner.