Why would a historian use a primary source when studying about a historical event?

Which fact would this be, and how might you verify the truth?

What was the first major route to connect europe and asia

Pls quickly! which of the following statements about spanish plantations is not accurate? a. spanish plantation screw sugarcane for export to spain. b. the spanish had a little concern for the lives of the indians who worked on the plantations. c. spanish presentation grew a wide variety of crops and sent the produce to many different european countries. d. to replace the native americans our dying off the spanish important african slaves.