Final answer:
Option B most effectively adds to the narrative by expressing the character's excitement and revealing the specific event, which is Samantha qualifying for the summer acting program. The line of dialogue that Casey should add to develop the character and event in Casey’s narrative is: “I made the cut!” she squealed. “I qualified for the summer acting program!”
Step-by-step explanation:
In the narrative excerpt provided, Casey is looking to develop the character and the event further by adding a line of dialogue. The most effective line to add would be the one that conveys the character's excitement and provides specific information relevant to the narrative's context. Therefore, option B, “I made the cut!” she squealed. “I qualified for the summer acting program!”, is the most suitable choice because it directly communicates Samantha's emotions and clearly explains the nature of the news she received. This adds to the buildup and allows for better understanding of the event's significance in the story.