Can someone plz explain what we should be doing by steps

Why are primary sources important when studying historical events

Which distinctive feature of the notre dame cathedral allowed it to accommodate its large stained glass windows? a. its barrel vaults b. its flying buttresses c. its quadrant arches d.its square bays

Me i really need which of these was an accomplishment of the han dynasty? the invention of the seismograph finding a water passage to europe the invention of the ballpoint pen the invention of the abacus