Answer: A combination of them all
Explanation: At the end of the day, the final decision and fault fall on Macbeth for dealing the blow and going through with it. Although, the pressure of these witches and Lady Macbeth would ultimately be the push of him killing.
She probably died from complications of her surgery.
Where the actors should stand
I want to say it is a, however d does sound right to me also. I know b and c are not right because it just doesnt make sense with the sentence. Overall I would say a because it sounds the most right.
Hope you get the answer right! and let me know what the real answer was because I'm interested to see whether it was a or d.