Answer:
A). Exposition.
Step-by-step explanation:
'Exposition' is defined as the element of the plot in which the author introduces the characters, setting, and background information to the readers which helps them understand the historical context in which the story is written and understand the narrative more effectively.
As per the question, the 'exposition' is demonstrated here as the author provides the introduction of the protagonist 'Sylvia' and description of the setting of the 'sidewalk', 'pretty fall day with leaves turning colors, falling off', etc. This allows the readers to have basic background information that the story is set in and hence, option A is the correct answer.