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 effectively heightens the sense of urgency and panic as it portrays Sylvia's struggle to escape and the pressing deadline of the bus leaving without her. It adds a layer of conflict and excitement to the narrative.