Final answer:
The most likely reason paragraph 4 in "Celeste's Heart" is a single sentence is to reveal Celeste's disappointment.
Step-by-step explanation:
The most likely reason paragraph 4 in "Celeste's Heart" is a single sentence is to reveal Celeste's disappointment. A single sentence can create a sense of abruptness or finality, which can effectively convey the feeling of disappointment. By using a single sentence, the author emphasizes Celeste's emotional state and highlights the impact of the event on her.