Conversation so far:
What part did Rosa Parks play in changing the law?
Rosa Parks rejected bus driver James F. Blake's order to relinquish her seat in the colored section to a white passenger, after the whites-only section was filled.
When did the Rosa Parks bus incident occur?
Rosa Parks rejected bus driver James F. Blake's order on December 1, 1955, in Montgomery, Alabama.
Did Rosa Parks give up her seat?
Rosa Parks rejected bus driver James F. Blake's order on December 1, 1955, in Montgomery, Alabama.

Question: What occured on the bus?
Self-contained rewrite: What occured on the bus that Rosa Parks was on?