This question is asking us about an Implication of a given detail.
@ Redefinition of the boundaries of Impressionism is mentioned in line 23 - 25. Since the question is asking what resulted in this, we should look at previous sentences. And the author talks about Herbert’s attempt to “restore Impressionist paintings to their sociocultural context.” Thus, we can see that the author implies Herbert’s attempt to place Impressionist paintings to a right (in his opinion) sociocultural text.
===== Answer Choices Analysis =====
A) This is the opposite of what Herbert is trying to do. He wants to emphasize "subject matter"
B) The passage is rather advocating that Herbert was trying to place Impressionism into the “right” context, and Herbert thought that 1860~1880 was the right one. Nothing bias-like opinion towards modern industry has been mentioned.
C) Making a direct identification, “sociocultural text”, this is the closest to the answer choice. Correct
D) If anything, his attempt in categorizing artists into Impressionist painting has been claimed “eccentric.” So, he didn’t try to include them all.
E) Whether he knew about it or was familiar with it was not mentioned.