D is correct counter means to receive then give back in a better way.
Iago is referring to the plan that he has been setting for Othello.
He says "Work on, <span>My medicine, work! " which shows that he's trying to make sure that the hints and comments he has dropped will take hold in Othello's mind so that he believes Desdemona and Cassio are having an affair. </span>
Answer: it's D, People can be their own worst enemies.
Explanation:
They should all be periods