Answer:
sure, uwu
Explanation:
I don't have much to say, ..> <
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.
I don't see the underline, but I'm pretty sure that the verb is "has known". That's the present perfect tense.
I believe it is called interjection:) good luck!