I believe the answer is: D. There are three economic classes: the rich, the poor, and the middle class.
The separation between these classes is based on their ownership of wealth&resources. The poor are those who barely have enough resources to keep living,
The middle class are those who can comfortably fulfil their basic needs while having a little bit of surplus that they can put into saving , while the Rich are those who had abundance of wealth & resources, to the point where they would not able to spend it in their lifetime.
The answer is Literacy increased among ordinary people.
I searched that just to make sure that I was right.
