How have geographic features allowed or blocked cultural diffusion?

i would think yes.

explanation:

because we have every natianlity in our country which makes us so diverse and unique. that's why in a lot of cities there are places like little italy, koreatown, chinatown.  

i would say b. research typically uses a variety of sources

there are indirect ways of affecting state laws   by with holding funding's. and that's why we have a 55mph speed on the high way with a design of 70mph speed.