Actually we can use the similar ways to understand B & E
B: "of an America whose ..." we can understand that "an America" here is different from another whose population was 70% rural and from another whose population was 50% rural.
E: dj used a similar way at E "A says immigrants entered the USA with a population, still, more than 90% rural"
However B makes more sense.
"Life is like a box of chocolates, you never know what you'r gonna get"