Which line of dialogue from act iii, scene i of romeo and juliet most foreshadows that mercutio’s death will lead to other tragic events in the story?

benvolio: o romeo, romeo! brave mercutio’s dead;
that gallant spirit hath aspir’d the clouds,
romeo: this day’s black fate on more days doth depend;
this but begins the woe others must end.
tybalt: thou wretched boy, that didst consort him here,
shalt with him hence.
prince: romeo slew him, he slew mercutio;
who now the price of his dear blood doth owe?

This day’s black fate on more days doth depend; / This but begins the woe others must end.

Explanation:

While Romeo and Juliet fall in love with each other, their families (the Montagues and the Capulets) do not stop hating each other.

This conflict culminates in Act III, Scene I, when Mercutio, Romeo's close friend, and Tybalt, Juliet's cousin, begin to fight. Romeo attempts to avoid fighting Tybalt, as he is now married to Juliet. When Tybalt murders Mercutio, Romeo loses patience and fights Tybalt, eventually killing him. Romeo's mentioning of 'black fate'  foreshadows other tragic events. He is aware that Mercutio's death (and Tybalt's) will have a negative impact on his relationship with Juliet, which is confirmed when Romeo is forced to flee.  In this way, Mercutio's death actually triggers a series of events which will lead to Romeo and Juliet's death.

the words “strangest” and “unusual” suggest that the narrator is about to tell the story of an odd or puzzling group of people.