The correct answer is the first sentence, In Romeo and Juliet, William Shakespeare demonstrates how the hatred between the Montague's and Capulet's leads to the deaths of young lovers. That is because the second is just a statement that would be elaborated in the paper, not a thesis. The third and the fourth are not it because they are not the theme of the play, since they don't try to end the feud, they just love each other, and also their marriage in secret is not important for the overall course of the play since it could've not happened and still the things would play out the same.
I did this before that's how I know the options, Hope it helps! :-)
