What discovery in the 15th century greatly advanced progress in science?

The answer for this question is: Printing press
The discovery of the printing press allow every scientists to publish the results of their experiments/studies.
This allow other scientists to obtain additional information from their seniors and make all scientific discoveries could be made at a much faster rate.

The social difference that caused sectionalism in the antebellum era would be c.)  north was disorganized. the north had slow population growth, where as the south had mass immigration.hope this really mark