What are differences between high income, middle income, and low income countries?

The main difference is that you would not live the same life in a low-income country as you would live in a higher income country.

For example lets take India and US

Most of the people in India would not able to afford an Audi but the people in the US would be able to afford one as it is cheaper and also have less taxes

answer; (d); skeletal muscles and sensory receptors;