Answer:
Giving the ability to read and write
Explanation:
If the slaves could read or write, there was a possibility of them freeing themselves by forging their owner's signature on a contract.
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
