<span>The correct answer is A. Romeo blames falling in love with Juliet as the cause of Mercutio's death.
After Mercutio dies, Romeo says, "O sweet Juliet, Thy beauty hath made me effeminate And in my temper soften'd valour's steel." Here, he is saying that, because he fell in love with Juliet, he became weak. His love softened "valour's steel" -- or the brave metal of a sword -- making him unable to fight his enemy Tybalt.
The implication is that, had he not fallen in love with Juliet, he would have been strong enough to fight Tybalt and his friend would not have died. Therefore he blames falling in love with Juliet as the cause of his friend's death.</span>
