The correct answer to this question is B, per capita GDP. It is used to compare countries economic output to one another. It compares this by its residents. It divides the economic output by the country's population. Per capita GDP, which stands for gross domestic product, can be used to compare any country to another.
The term per capita is a Latin phrase, which means for each individual or person. To put per capita GDP in presepective, China has a low rank because it has a large population. However, United States ranks higher because it has much fewer people than China has.