Answer:
A. increased; Great Migration
Explanation:
When the migration began, 90 percent of all African-Americans were living in the South. By the time it was over, in the 1970s, 47 percent of all African-Americans were living in the North and West. A rural people had become urban, and a Southern people had spread themselves all over the nation.
Wind, solar, and hydroelectric power are all eco friendly
What you're looking for in here is the hardness: a material can scratch another material if it's harder than it.
So the desired material cannot be harder than amphibole, which has a hardness of 6.
But it has to be harder than fluorite, which has a hardness of 4.
So we're looking for a hardness of between 4 and 6 and from the table we see it's magnesite (we'll need a hard magesite) - this is the correct answer!
