In your opinion, what event in Act III causes the greatest increase in suspense? Explain your answer.

I'd have to go with the Tybalt/Romeo fight in scene 1. Tybalt is bent on an all out brawl with Romeo. Romeo insists they are now family. Tybalt is really confused but still wants to fight. Mercutio intervenes and the situation becomes really out of hand. Here we can see the tragedy begin to unravel before us.