AP Lit if you know this answer help me please. its about William Shakespear and its hella boring jk rob my points

Why are radio observatories located in valleys far away from urban centers? a. to shield them from electromagnetic interference b. to avoid sound pollution c. to avoid disturbing people living in the city d. to shield them from water vapor

Why is it essential to operationally define the variables in a study?

This is an ap world history question. i am working on a worksheet which has a vent diagram with each circle labeled either us or byzantine economy. the middle is the similarities. can someone explain to me the similarities and especially the differences between the two?