21. What is the difference between primary and secondary sources? O a. Primary sources are written about an event later by someone who was not there; secondary sources are written or created by people who were actually there. b. Primary sources are journals or letters from people who lived through an event; secondary sources are written by people who were actually there. c. Primary sources are things like biographies; secondary sources are things like history books and historical essays. d. Primary sources are written or created by people who were actually there; secondary sources are written about an event later by someone who was not there.

21. What is the difference between primary and secondary sources? O a. Primary sources are written about an event later by someone who was not there; secondary sources are written or created by people who were actually there. b. Primary sources are journals or letters from people who lived through an event; secondary sources are written by people who were actually there. c. Primary sources are things like biographies; secondary sources are things like history books and historical essays. d. Primary sources are written or created by people who were actually there; secondary sources are written about an event later by someone who was not there.