Premises:
1) Mona Lisa -> arguably world's most famous painting
2) Mona Lisa is neither flawless nor incomparable
3) Hands are badly matched, background is dull and other portraits from the same period evince equally enigmatic expressions
Conclusion:
4) Undue focus on Mona Lisa + Popularity of a few other pieces prevents most people from seeing the painting for what it really is and also from understanding the true scope of 15th and 16th Century Eurpoean painting.
We need a statement that supports this conclusion.
A. Most people do not believe that the Mona Lisa has any evident flaws
C. It is possible for most people to understand the scope of 15th and 16th century European painting
We can immediately discard B, D and E as they are unsupported by the passage and do nothign to support the conclusion.
A can be taken out as well, as the conclusion is not about criticizing the Mona Lisa, or about people's ability to discern flaws in the Mona Lisa. Rather, it's lamenting that unfair focus on a few masterpieces of the 15th and 16th century prevents people from really understanding the true scope of paintings during those two periods.
C is the best choice. It says people are able to understand the scope of 15th and 16th centruy European painting. This choice alone supports the conclusion made by the passage.