If you lived in philadelphia in the 11780s whats the fewest number of miles would you have to travel

d. the polar jet stream   lies between the polar easterlies and trade winds should be your answer

the factors that the economies of the muslim empires prosper were:

1- land trade routes-located between three continents  

2- sea trade routes

trade contributed to the spread of muslim empires, and with that islamic culture led to a growing feeling of internationalism resulted in the transfer of technology, science, and other cultural forms.

i believe your answer is mountains.