Mercutio's announcement anticipates the happening to his demise, which results in Romeo getting to be offended because Tybalt just slaughtered Mercutio, Romeo's great companion. This makes Romeo murder Tybalt, which prompts his expulsion, etc. The following event, Mercutio's death, similarly marks the cause of other tragics events.
D. Ledger lines are used to extend musical staff. I think my answer is correct because ledger lines represent notes that surpass the bottom and up limits.