Why would a researcher use a primary source instead of a secondary source when analyzing a a historical event

Which plan proposed to maintain open trade between china and western nations? open door policy national sovereignty missionary diplomacy salutary neglect

Which impact did the civil war have on the spread of disease in texas a. disease decreased bc people left the area to fight in the war b. disease increased bc medicine was in short supply. c. disease increased bc many new diseases were brought to the area d. disease decreased bc confederate doctors distribute new medicines to local communities

The zealots were for a: the teaching of jesus b: temple and sacrifices c: faith and law d: the military overthrow of roman rulers