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.
The correct answer in this question is option B. The phrase "inward eye" refers to the mind of Wordsworth. He has the capability to imagine things distinctly in his mind. This is his visual imagination and it explains why he is a great poet.
