When, where, and by whom were vaccines for polio developed? which vaccine is most effective, and why?

(05.04 mc) how did the roman transportation system keep the empire strong? plz

Describe the geography of the nile valley . how did this geography affect civilizations that emerged in the nile valley

The major impact third parties have on presidential elections has been to.. a. encourage larger vote turnout b. recruiter leader from the democratic and republican party to run for president c. generate increased party identification among the electorate d. developing issues that are later adopted by the major political parties e. drawn off of votes from the major parties to throw election into the house representatives