What Is the United States Government's Formal Definition of the Poverty

What is the United States government's formal definition of the poverty line?

A) It is a level of annual income equal to total income in society divided by the population, adjusted for a family of four.
B) It is a level of annual income equal to the amount of money necessary to purchase the minimum quantity of food required for adequate nutrition.
C) It is the annual income level below which a household is exempt from taxes.
D) It is a level of annual income equal to three times the amount of money necessary to purchase the minimum quantity of food required for adequate nutrition.