The paragraph that would help build tension if added to the story is:
"As she struggled to free herself, the bus pulled into view. She waved her arms wildly, but the driver didn’t notice her. And she was still stuck. What was she going to do? She could not be late to school today."
This paragraph heightens the urgency and stress of the situation, emphasizing Sylvia's desperation as she struggles against the clock and the obstacles in her way.