It grew exponentially in this period because in the aftermath of the second world war, there was a baby boom as a result of numerous young couples created by high amounts of returning soldiers.
This is a long question please rephrase it.
The answer is Erosion, which is the the gradual destruction or diminution of something -- in this case, rocks. I hope this helps! For reference/perspective, sand is the product of rock erosion, because it's really just tiny remnants of crushed rock. Those "small pebbles" could be sand, but you'd have to emphasize just how small they are -- one grain of sand is just that: a grain
Here's a reason why: Africans were strangers to the Americans. Because the Africans were poor, they didn't have any allies to watch out for them or to protect them.
