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 enhances the urgency of the situation and heightens the tension as it shows Sylvia's struggle against time and her fear of being late.