The dialogue option that best helps develop both characters is:
“We’re going to have so much fun,” Sadie said. “I bet we’ll get to meet the band. I bet we’ll even get to hang out with them!”
“We probably won’t even get to go,” Marco said. “I bet the whole show will get canceled and we’ll have a terrible day.”
This selection effectively showcases Sadie's optimism and excitement, highlighting her tendency to look for positive outcomes and make grand predictions about fun experiences. In contrast, it captures Marco's skeptical and brooding nature, as he immediately dampens Sadie's enthusiasm with a pessimistic outlook. This contrast between the characters' personalities is clearly established through their dialogue.