"my last duchess" reveals that the duke was irritated by the fact that his wife a. beautiful. b. demanding. c. not discriminating. d. dependent on him.

I have never read the story, but I just looked up some summaries about it and what the theme was.
So I would say the answer was either A or C. (I think it might be C)

The correct option is C.
'My Last Duchess' is a poem written by Robert Browning and it talks about a Dutch, who is about to marry another wife after the death of his wife. In the process of showing his palace to the visitors from the new wife family, they come across the portrait of the Dutch's late wife. During this period, it becomes obvious that the Dutch detest the behavior of his late wife because she flirt with everyone. She smiles to everyone and does not discriminate against anyone.The Duchess considered this behavior as been disgraceful.  

Conclusion is the answer

My favorite candy is gummy bear