C. It is sometimes too difficult to define something that is easily recognized
Explanation:
A. is an opinion and has nothing to do with the text at all.
B. is not the main focus in the paragraph but only one line which is used to explain the main idea.
D. is not mentioned anywhere in the text, experts are called experts for a reason. The text does not suggest that ordinary people know as much as experts.
So the Answer is C; The whole paragraph is talking about how there isn't one specific definition and the last sentence mentions how people just know when they see one.
