An appropriate summary for the article "A Most Troublesome Element" is the last option - C. Arsenic is a naturally occurring, poisonous element that has threatened the health of humans since the Middle Ages.
It clearly states what the whole article is about.
Answer:
I think it's the second one the search engine looks through all the text on the internet for a direct match to the words you typed
C. to mock the manner of speaking that the writer is criticising
