What are the biggest impact of jonas salk's work with poliomyelitis?

How did presidential reconstruction allow black codes to be passed

As societies modernize, what often happens to crime rates? a. they increase b. they decrease c. they remain the same d. they increase slightly and then fall rapidly

Initially, northerners did not want missouri to be included in the union because 1.) maine would not be allowed to enter the union as a free state 2.) missouri wanted to enter the union as a free state 3.) missouri wanted to enter the union as a slave state 4.) maine would not be allowed to enter the union as a slave state