Historians use primary and secondary sources to collect historical evidence. what is the difference between these two sources?

Primary sources are sources that are directly from the time that an event took place that can give first hand knowledge about an event or occurrence. These include newspaper articles, video footage, or a personal account from an individual who was there when a historical event took place. Whereas a secondary source is a step removed in that the author is analyzing primary sources or is writing from a position where they don't possess direct knowledge to an event but are using historical evidence to provide a perspective on a particular issue or historical event. 

The correct answer is b

He droped it over the bridge into the river