Answer:
D. Othello is weakened by sadness.
Step-by-step explanation:
"I'd have thee live; For in my sense, 'tis happiness to die"
Othello is so sad that killing Iago would be a free pass. Othello's desire is to have Iago living with all the disgrace, guilt, and shame that he managed to collect so someone will feel as disgraced as Othello does, perhaps. Specially the one responsible for all.