How does an economist compare the standard of living in two different countries? by looking at the quality of life
by comparing real GDP per capita
by seeing how the GDP is distributed
by measuring physical capital

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.

it should be d or b but i'm sure it's d

answer; involves both the element of performance and interpersonal interactions;